Leg joint assist device for leg type movable robot

ABSTRACT

An assist device that applies an auxiliary driving force to a joint in parallel with a driving force of a joint actuator between a thigh portion and a crus portion, which are a pair of link members of a leg. The assist device generates the auxiliary driving force by use of spring device, such as a solid spring or an air spring. A member supporting a rod member connected to the spring device is provided with a device for transmitting a bending and stretching motion of the leg at the joint (a relative displacement motion between the thigh portion and the crus portion) to the spring device to generate an elastic force of the spring device, and for discontinuing the transmission of the bending and stretching motion to the spring device. This transmitting device is controlled in accordance with a gait of a robot. Thus, a burden on the joint actuator is reduced where necessary and favorable utilization efficiency of energy can be stably ensured.

TECHNICAL FIELD

[0001] The present invention relates to a leg joint assist device whichgenerates an auxiliary driving force to a joint of a leg of a leggedmobile robot such as a biped mobile robot, to assist a joint actuatorwhich is for driving the joint.

BACKGROUND ART

[0002] In a legged mobile robot with a plurality of legs, each of thelegs is configured by sequentially connecting a plurality of linkmembers through a plurality of joints from a body. For example, in abiped mobile robot with two legs like a human, each of the legs isconfigured by sequentially connecting the link members, which correspondto a thigh portion, a crus portion, and a foot portion, through a hipjoint, a knee joint, and an ankle joint, respectively, from a body ofthe robot. In addition, in the legged mobile robot of this kind, amotion of each of the legs for moving the robot is produced by applyinga driving force (torque) to each of the joints of each of the legs byusing a joint actuator such as an electric motor.

[0003] Incidentally, in the mobile robot of this kind, when, forexample, a movement speed thereof is increased, forces (moment) actingon the joints of each of the legs are likely to be relatively large in afoot landing state of each of the legs (a state of a supporting legperiod of each of the legs), due to floor reaction forces or the like.Consequently, driving forces (torque), which should be generated to thejoint actuators to resist the forces, are likely to be relatively large.For example, in a case of allowing the biped mobile robot to run with agait (a motion pattern of legs) similar to the gait of a running human,the driving force to be generated to the joint actuator of the kneejoint becomes large, particularly in a supporting leg period of each ofthe legs, according to the knowledge of the inventor and the like. Inthis case, when the joint actuator is an electric motor, theaforementioned driving force is generated by a regenerative operation ora powering operation of the electric motor. With-any of theseoperations, however, it is required to energize the electric motor or apower source such as a battery with a high current. Thus, an energy lossby Joule heat or the like is likely to be large. Further, since theelectric motor with a large capacity is required, the size and weight ofthe electric motor become large.

[0004] Meanwhile, as disclosed in Japanese Patent Laid-Open PublicationNo. 2001-198864 (especially FIG. 9 of this publication), for example, abiped mobile robot is known in which a spring is provided between twolink members (a thigh portion and a crus portion) connected by a kneejoint of each leg.

[0005] While moving horizontally, this biped mobile robot convertskinetic energy in the horizontal direction of the robot into elasticenergy of the spring and stores the elastic energy, thus producing ajumping motion of the robot by the use of the elastic energy. In thebiped mobile robot provided with the springs as above, a part of adriving force to be generated in each of the knee joints is provided bythe elastic force of the spring during a part of the period when therobot is in the running motion or the like.

[0006] Thus, a burden on the joint actuators of the knee joints can bereduced. However, in this biped mobile robot, the elastic force of thespring is always acting between the thigh portion and the crus portionof each of the legs. Therefore, while the biped mobile robot is moving,a situation occurs where the elastic force of the spring acts in anopposite direction to the driving force which should be generated ineach of the knee joints. In such a situation, a driving force generatedto the joint actuator of each of the knee joints becomes unnecessarilylarge. As a result, it becomes difficult to improve utilizationefficiency of the total energy of the robot.

[0007] The present invention was accomplished in light of theabove-described circumstances, and it is an object of the presentinvention to provide a leg joint assist device for a legged mobilerobot, which is enabled to reduce burdens on joint actuators asnecessary and to stably ensure favorable utilization efficiency ofenergy.

DISCLOSURE OF THE INVENTION

[0008] A novel leg joint assist device for a legged mobile robot is aleg joint assist device for generating an auxiliary driving force on aspecific joint of a legged mobile robot in parallel with a driving forceof a joint actuator driving the specific joint, the robot comprising aplurality of legs, extending from a body, configured by connecting aplurality of link members sequentially from a body side through theplurality of joints, wherein at least one joint amongst a plurality ofthe joints of each of a plurality of the legs is defined as the specificjoint in the legged mobile robot, the leg joint assist devicecomprising: spring means, provided to be able to transmit a relativedisplacement motion of a pair of the link members connected by thespecific joint, the relative displacement motion being caused byactuation of the specific joint, for generating the auxiliary drivingforce while storing elastic energy in synchronization with the relativedisplacement motion in a state where transmission of the relativedisplacement motion is continued, and for restoring a state where theelastic energy is released in a state where transmission of the relativedisplacement motion is discontinued; motion transmissioncontinuation/discontinuation means for continuing and discontinuingtransmission of the relative displacement motion of the pair of linkmembers to the spring means; and control means for controllingcontinuation/discontinuation of transmission of the relativedisplacement motion to the spring means by the motion transmissioncontinuation/discontinuation means, depending on a state of motion ofeach of the legs.

[0009] According to the present invention described above, the leg jointassist device includes the motion transmissioncontinuation/discontinuation means for continuing/discontinuingtransmission of the relative displacement motion of the pair of linkmembers, caused by the actuation of the specific joint, to the springmeans. Further, in a state where transmission of the relativedisplacement motion of the pair of link members is discontinued, thespring means restores the state where the elastic energy is released (astate equivalent to a natural length state of a coiled spring). Thus, bycontrolling the motion transmission continuation/discontinuation meansby use of the control means depending on the state of motion of each ofthe legs, it becomes possible to cause the spring means to generate theauxiliary driving force in a state where the auxiliary driving force bythe spring means is required (for example, a state where a driving forcewhich should act on the specific joint is relatively large and thespring means can generate the auxiliary driving force in the samedirection to the driving force). It also becomes possible to prevent thespring means from generating the auxiliary driving force in a stateother than the above.

[0010] Hence, according to the present invention, a burden on the jointactuator can be reduced when necessary. As a result, it becomes possibleto allow the legged mobile robot to move with various kinds of gaitswhile using a relatively small joint actuator. In addition, due to therelative displacement motion of the pair of link members, the springmeans stores the elastic energy which generates the auxiliary drivingforce. Thus, it becomes possible that the auxiliary driving force isgenerated while effectively utilizing kinetic energy of the robot. As aresult, utilization efficiency of the entire energy of the robot can beimproved.

[0011] Note that, in a biped mobile robot having two legs like a human,it is preferred that the specific joint be a knee joint.

[0012] In the invention described above, it is preferred that thecontrol means control the motion transmissioncontinuation/discontinuation means to discontinue transmission of abending and stretching motion of the pair of link members to the springmeans at least during a first predetermined period in a state where eachof the legs is lifted off a floor. In general, the driving force to begenerated at each of the joints of each of the legs is relatively smallin the state where the each of the legs is lifted off the floor (a stateof free leg period of each of the legs). If the auxiliary driving forceby the spring means is generated in such a state, the auxiliary drivingforce becomes larger than the driving force originally required for thespecific joint. This is likely to result in a situation where a furtherexcessive driving force must be generated to the joint actuator of thespecific joint, in order to reduce the auxiliary driving force.Therefore, in the present invention, transmission of the relativedisplacement motion to the spring means is discontinued at least duringthe first predetermined period in the state where each of the legs islifted off the floor, so that the auxiliary driving force by the springmeans is not generated. Thus, the excessive driving force is notgenerated in the joint actuator, thereby reducing energy consumed by thejoint actuator. Further, the auxiliary driving force by the spring meansis not generated during the first predetermined period in the statewhere each of the legs is lifted off the floor. Thus, a posture of eachof the legs is not affected by the spring means, and thereby the stateof the posture of each of the legs is stably controlled to be in adesired state of the posture.

[0013] Moreover, in the present invention, preferably, while the leggedmobile robot is moving with a predetermined gait which has been decidedin advance, the control means controls the motion transmissioncontinuation/discontinuation means to continue transmission of thebending and stretching motion of the pair of link members to the springmeans at least during a second predetermined period in a state whereeach of the legs lands on the floor. Specifically, the auxiliary drivingforce by the spring means is not necessarily always generated in thestate where each of the legs lands on the floor while the legged mobilerobot is moving. Basically, it is preferred that the auxiliary drivingforce be generated under a situation where the driving force to begenerated to the specific joint of each of the legs becomes relativelylarge. Therefore, the relative displacement motion is transmitted to thespring means at least during the second predetermined period in thestate where each of the legs lands on the floor, while the robot ismoving with the predetermined gait. Thus, the auxiliary driving forcecan be generated by the spring means only in the situation where theauxiliary driving force is required.

[0014] In this case, it is preferred that the second predeterminedperiod in the state where each of the legs lands on the floor bedetermined such that relative displacement amounts between the pair oflink members at start time and stop time of the second predeterminedperiod are approximately the same. Specifically, if the relativedisplacement amounts at the start time and the stop time of the secondpredetermined period are largely different from each other, the springmeans cannot entirely release the elastic energy at the stop time of thesecond predetermined period. Therefore, since the auxiliary drivingforce of the spring means is not sufficiently small yet, the auxiliarydriving force to be acted on the specific joint by the spring meansbecomes discontinuous at the stop time of the second predeterminedperiod. In the case like this, an inappropriate variation of thebehavior (a non-smooth change in the behavior) of each leg of the robotoccurs easily. Additionally, free vibration occurs from the stop time ofthe second predetermined period, especially when the spring means is asolid spring such as a coiled spring. Thus, when starting transmissionof the relative displacement motion of the pair of link members to thespring means thereafter, the auxiliary driving force which is acted onthe specific joint by the spring means is discontinuously changed andthe like. Therefore, the auxiliary driving force may becomeinappropriate. Hence, in the present invention, the second predeterminedperiod is determined such that the relative displacement amounts betweenthe pair of link members at the start time and stop time of the secondpredetermined period become approximately the same. Accordingly, thespring means is in the state where the elastic energy is released (astate where the auxiliary driving force of the spring means is about“0”) at the stop time of the second predetermined period during whichthe auxiliary driving force by the spring means is generated. Therefore,it is possible to avoid a situation where the auxiliary driving force tobe acted on the specific joint by the spring means discontinuouslychanges at the stop time of the second predetermined period at whichtransmission of the relative displacement motion to the spring meansstops. It is also possible to avoid a situation where free vibrationoccurs from the stop time of the second predetermined period.Consequently, the legs of the robot can be actuated with smoothbehavior.

[0015] In the present invention in which the auxiliary driving force bythe spring means is generated in the state where each of the legs landson the floor while the robot is moving with the predetermined gait asmentioned above, it is preferable that means for controlling a drivingforce of the joint actuator is provided such that, while the motiontransmission continuation/discontinuation means is continuingtransmission of the relative displacement motion of the pair of linkmembers to the spring means, a sum of the auxiliary driving force by thespring means and the driving force of the joint actuator becomes adesired driving force determined to follow a desired gait of the leggedmobile robot.

[0016] According to the above, the total driving force acting on thespecific joint is controlled to be the desired driving force determinedto follow the desired gait of the robot (a required value of the drivingforce which should be generated to the specific joint to allow the gaitof the robot to follow the desired gait) regardless of whether theauxiliary driving force by the spring means is being generated. Thus,the operation of the robot can be performed smoothly.

[0017] Moreover, the means for controlling the driving force of thejoint actuator as mentioned above estimates the auxiliary driving forceby the spring means based on a variation of the relative displacementamount between the pair of link members from the start time of thesecond predetermined period and characteristic data of the auxiliarydriving force of the spring means, which is obtained in advance.

[0018] Specifically, the auxiliary driving force changes depending onthe variation of the relative displacement amount between the pair oflink members from the start time of the second predetermined period. Inaddition, the form of the variation depends on the characteristics ofthe spring means. Therefore, by estimating the auxiliary driving forceby the spring means in the above-mentioned manner, an appropriateestimated value of the auxiliary driving force can be obtained.Consequently, the driving force of the joint actuator can beappropriately controlled. Note that the auxiliary driving force by thespring means can be detected directly by the use of a force sensor orthe like.

[0019] Moreover, in the present invention, the spring means may be asolid spring such as a coiled spring, a leaf spring, a torsion spring, ametal spring, rubber and the like, as a matter of course. However, it ispreferred that the spring means be a gas spring which elasticallygenerates the auxiliary driving force by compression and expansion ofgas. Specifically, the gas spring unlikely to cause free vibration incomparison with the solid spring. Therefore, free vibration of thespring means can be prevented especially when transmission of therelative displacement motion to the spring motion is discontinued. Thus,when the transmission of the relative displacement motion to the springmeans is re-started after transmission thereof has been discontinued,the desired auxiliary driving force of the spring means can be generatedsmoothly.

[0020] Moreover, in the present invention, it is preferred that thejoint actuator be an electric motor. Specifically, in the presentinvention, the burden on the joint actuator of the specific joint can bereduced as described earlier. Therefore, a current flowing through theelectric motor serving as the joint actuator can be small, and an energyloss due to Joule heat or the like can be minimized. In addition, theuse of the electric motor as the joint actuator can realize smoothmotion control of the legs of the robot. Furthermore, a vibrationcomponent of the motion of the legs caused by the spring means can beeasily diminished by control of the electric motor, without providing amechanical buffering device (damping device), especially in a state ofgenerating the auxiliary driving force by the spring means. Thus, stablecontrol of the motion of the robot can be smoothly performed.

BRIEF DESCRIPTION OF THE DRAWINGS

[0021]FIG. 1 is an explanatory view showing the entire structure of alegged mobile robot in a first embodiment of the present invention;

[0022] FIGS. 2(a) and 2(b) are explanatory views exemplifying springmeans of an assist device provided in the robot in FIG. 1;

[0023] FIGS. 3(a) and 3(b) are cross sectional views showing aconfiguration of an essential part of the assist device provided in therobot in FIG. 1;

[0024]FIG. 4 is a diagram showing characteristics of the spring meansprovided in the robot in FIG. 1; and

[0025]FIG. 5 is a block diagram showing a functional configuration of acontrol unit provided in the robot in FIG. 1.

[0026]FIG. 6 is a flowchart showing processing by the control unitprovided in the robot in FIG. 1;

[0027]FIG. 7 is a flowchart showing subroutine processing of anessential part of the flowchart in FIG. 6; and

[0028]FIG. 8 is a diagram for explaining actuation of the assist deviceprovided in the robot in FIG. 1.

[0029]FIG. 9 is a diagram for explaining actuation of an assist devicein a second embodiment of the present invention;

[0030] FIGS. 10(a) and 10(b) are cross sectional views showing aconfiguration of an essential part of an assist device in a thirdembodiment of the present invention;

[0031]FIG. 11 is a diagram showing characteristics of spring meansprovided in the assist device in FIG. 10;

[0032] FIGS. 12(a) and 12(b) are cross sectional views showing aconfiguration of an essential part of an assist device in a fourthembodiment of the present invention; and

[0033]FIG. 13 is an explanatory view showing a configuration of anassist device in a fifth embodiment of the present invention.

[0034]FIG. 14 is an explanatory view showing a configuration of anassist device in a sixth embodiment of the present invention;

[0035]FIG. 15 is a cross sectional view showing a configuration of anessential part of the assist device in FIG. 14;

[0036]FIG. 16 is an explanatory view showing a configuration of anassist device in a seventh embodiment of the present invention;

[0037]FIG. 17 is a cross sectional view showing a configuration of anessential part of the assist device in FIG. 16;

[0038]FIG. 18 is an explanatory view showing a configuration of anassist device in an eighth embodiment of the present invention;

[0039]FIG. 19 is a cross sectional view showing a configuration of anessential part of the assist device in FIG. 18;

[0040]FIG. 20 is an explanatory view showing a configuration of anassist device in a ninth embodiment of the present invention; and

[0041]FIG. 21 is an explanatory view showing a configuration of anassist device in a tenth embodiment of the present invention.

[0042]FIG. 22 is an explanatory view showing a configuration of anassist device in an eleventh embodiment of the present invention;

[0043]FIG. 23 is a diagram showing characteristics of spring meansprovided in the assist device in FIG. 22;

[0044]FIG. 24 is a diagram showing characteristics of spring meansrelated to a modified aspect of the eleventh embodiment;

[0045]FIG. 25 is an explanatory view showing a configuration of anassist device in a twelfth embodiment of the present invention;

[0046]FIG. 26 is an explanatory view showing a configuration of anassist device in a thirteenth embodiment of the present invention; and

[0047]FIG. 27 is a cross sectional view showing a configuration of anessential part of the assist device in FIG. 26.

BEST MODE FOR CARRYING OUT THE INVENTION

[0048] A first embodiment of the present invention is described withreference to FIGS. 1 to 8. FIG. 1 is a schematic view depicting aconfiguration of a biped mobile robot as the legged mobile robot of thisembodiment. As illustrated, the robot 1 is provided with two legs 3 and3 extending downward from a body 2. Note that these legs 3 and 3 havethe same structure and thus one of the legs 3 (the forward-left leg 3 ofthe robot 1 in the figure) is shown only partially.

[0049] Similarly to the leg of a human, each of the legs 3 is configuredby sequentially connecting a thigh portion 4, a crus portion 5, and afoot portion 6 through a hip joint 7, a knee joint 8, and an ankle joint9, respectively, from the body 2. To be more specific, the thigh portion4 of each of the legs 3 extends from the body 2 through the hip joint 7,the crus portion 5 is connected to the thigh portion 4 through the kneejoint 8, and the foot portion 6 is connected to the crus portion 5through the ankle joint 9. Note that respective ones of the thighportion 4, the crus portion 5 and the foot portion 6 correspond to linkmembers in this invention.

[0050] In this case, the hip joint 7 is enabled to have rotationalmotions about three axes in directions of front and back, right andleft, and top and bottom of the robot 1. The knee joint 8 is enabled tohave a rotational motion about one axis in the right and left direction.The ankle joint 9 is enabled to have rotational motions about two axesin the directions of front and back, and the right and left. Because ofthe rotation motions of each of the joints 7, 8 and 9, each of the legs3 can have a motion which is almost the same as that of the leg of thehuman. In addition, the knee joint 8, for example, is provided with anelectric motor 10 (hereinafter, referred to as a knee joint electricmotor 10) as a joint actuator in order to perform the rotational motionabout one axis in the right and left direction. Further, although notillustrated, the hip joint 8 is provided with three electric motors forperforming the rotational motions about the three axes, respectively.The ankle joint 9 is provided with two electric motors for performingthe rotational motions about two axes, respectively.

[0051] Note that, in this embodiment, each of the foot portions 6 isconnected to the ankle joint 9 through a six-axis force sensor 11 inorder to detect a floor reaction force (translational forces inthree-axis directions of front and back, right and left, and top andbottom of the robot 1 and moments about the three axes) acting on eachof the foot portions 6. Moreover, each of the joints 7, 8 and 9 isprovided with an encoder (not shown) for detecting a rotation positionthereof (specifically, a rotation angle of the electric motor of each ofthe joints 7 to 9).

[0052] In this embodiment, the knee joint 8 of each of the legs 3 is aspecific joint in this invention, and an assist device 12 for applyingan auxiliary driving force to the knee joint 8 as necessary is providedin each of the legs 3.

[0053] The assist device 12 is provided with a rod member 14 connectedto the crus portion 5 through a free joint 13, a rod member 16 connectedto the rod member 14 through spring means 15, and a rod insertion member17 through which the rod member 16 is inserted to be movable in an axisdirection thereof. The rod member 14, the spring means 15, the rodmember 16 and the rod insertion member 17 as a whole extend upwardalmost along the thigh portion 4 from the free joint 13 of the crusportion 5. The circumference portion of the rod insertion member 17 isconnected to the thigh portion 4 through a free joint 18.

[0054] Here, the spring means 15 is enabled to store elastic energy. Forexample, a solid spring which generates an elastic force by elasticdeformation thereof or a gas spring which generates an elastic force bycompression and expansion of gas such as air can be used as the springmeans 15. The solid spring includes a coiled spring, a leaf spring, atorsion spring, rubber and the like. The gas spring includes a bag madeof rubber or the like in which a gas such as air is sealed, a cylinderwith a piston where the gas is sealed and the like. Further, the springmeans 15 is connected to the rod members 14 and 16 so as to generate anelastic force corresponding to a change of spacing between these rodmembers 14 and 16.

[0055] To be more specific, when, for example, a coiled spring which isa solid spring is used as the spring means 15, both ends of a coiledspring 19 are joined to the rod members 14 and 16, respectively, asshown in FIG. 2(a) . Alternatively, when, for example, a gas springhaving a cylinder configuration is used as the spring means 15, the rodmember 14 is joined to a cylinder 20 and the rod member 16 is joined toa piston 21 as shown in FIG. 2(b). The piston 21 is slidable within thecylinder 20 in an axis direction thereof. Gas such as air is then sealedwithin gas chambers 22 and 23 formed within the cylinder 20 above andbelow the piston 21. Note that, in this case, the rod members 14 and 16may be joined to the piston 21 and the cylinder 20, respectively, inreverse to the above. In addition, one of the gas chambers 22 and 23within the cylinder 20 may be opened to, for example, the atmosphere.

[0056] Note that, in the description below, a state where the springmeans 15 has released the elastic energy thereof (state where no elasticforce is generated) is referred to as a natural length state of thespring means 15 as a matter of convenience.

[0057] As further shown in FIGS. 3(a) and 3(b), the foregoing assistdevice 12 is provided with a lock mechanism 24 which latches the rodmember 16 so that the rod member 16 cannot move relative to the rodinsertion member 17. This lock mechanism 24 corresponds to motiontransmission continuation/discontinuation means in this invention andhas the following configuration. In one side portion of the rod member16, a plurality of recesses 16 a are provided at intervals in thelongitudinal direction thereof (a movable direction of the rod member16). Further, the rod insertion member 17 is provided with a latch pin25 to be able to move forward and backward to the side portion of therod member 16 having the above-mentioned recesses 16 a. By the forwardand backward movement, the latch pin 25 can be fitted into each of therecesses 16 a of the rod member 16 as shown FIG. 3(b). In this case, thelatch pin 25 is moved forward and backward by energization control of,for example, an electromagnetic solenoid 26. By fitting the latch pin 25into the recess 16 a, the lock mechanism 24 latches the rod member 16 sothat the rod member 16 cannot move relative to the rod insertion member17.

[0058] With the above-mentioned configurations of the assist device 12and the lock mechanism 24, in the state where the latch pin 25 of thelock mechanism 24 is moved backward (state of FIG. 3(a)), the rod member16 can be freely moved integrally with the spring member 15 and the rodmember 14 in the axis direction of the rod member 16 (hereinafter, theabove state is referred to as a free state) in synchronization with abending and stretching motion of the thigh portion 4 and the crusportion 5 at the knee joint 8 (this motion corresponds to a relativedisplacement motion in this invention and hereinafter referred to as aknee bending and stretching motion). In this free state, the kneebending and stretching motion is not transmitted to the spring means 15,and the spring means 15 is kept in an almost natural length state.Therefore, in the free state, an elastic force is not applied to theknee joint 8 of the leg 3 from the spring means 15.

[0059] Alternatively, when the latch pin 25 is moved forward during theknee bending and stretching motion so that the latch pin 25 is fittedinto one of the recesses 16 a of the rod member 16, the rod member 16 islatched so as not to be moved relative to the rod insertion member 17from when the latch pin 25 is inserted (hereinafter, this state isreferred to as a locked state). In this locked state, the spring means15 is compressed or extended from the natural length state by the kneebending and stretching motion. The spring means 15 then stores elasticenergy and generates an elastic force. Thereafter, the elastic forceacts on the knee joint 8 as a rotation force (auxiliary driving force)of the knee joint 8 in parallel with a rotation force of the knee joint8 by the foregoing knee joint electric motor 10. In this case, therotation force of the knee joint 8 by the spring means 15 (hereinafter,referred to as an auxiliary knee rotation force) depends on a variationof a bending angle θ between the thigh portion 4 and the crus portion 5(hereinafter, referred to as a knee bending angle θ; see FIG. 1) from aknee bending angle at start time of the locked state (transition fromthe free state to the locked state) (hereinafter, referred to as a lockstart knee bending angle).

[0060] More specifically, referring to FIG. 4, if the lock start kneebending angle is “θ1,” the auxiliary knee rotation force by the springmeans 15 changes relative to the knee bending angle θ with, for example,characteristics shown by a solid line a in FIG. 4. Further, if the lockstart knee bending angle is “2” (θ1>θ2), the auxiliary knee rotationforce by the spring means 15 changes relative to the knee bending angleθ with characteristics shown by a solid line b in FIG. 4. Here, the kneebending angle θ in this embodiment is an inclination angle of the axisof the crus portion 5 with reference to the axis of the thigh portion 4as shown in FIG. 1. The more the leg 3 bends at the knee joint 8, thelarger the knee bending angle θ becomes. Moreover, the auxiliary kneerotation force by the spring means 15 at the knee joint 8 in a bendingdirection of the leg 3 is expressed by a positive value, and the same ina stretching direction of the leg 3 is expressed by a negative value.Therefore, when the knee bending angle θ is decreased from the foregoinglock start knee bending angle (in a motion in the stretching directionof the leg 3), the auxiliary knee rotation force by the spring means 15increases in the bending direction of the leg 3. When the knee bendingangle θ is increased from the lock start knee bending angle (in a motionin the bending direction of the leg 3), the auxiliary knee rotationforce by the spring means 15 increases in the stretching direction ofthe leg 3. Furthermore, the smaller the lock start knee bending angleis, the larger the auxiliary knee rotation force at each of the kneebending angles θ becomes in the stretching direction of the leg 3. Inaddition, the auxiliary knee rotation force by the spring means 15 atthe lock start knee bending angle is almost “0.”

[0061] Note that the characteristics of the change of the auxiliary kneerotation force (curves of the solid lines a and b in FIG. 4) relative tothe change of the knee bending angle θ are uniform at any lock startknee bending angle. Moreover, in the foregoing free state, the springmeans 15 is in the natural length state as mentioned earlier. Thus, theauxiliary knee rotation force by the spring means 15 is almost “0” atany knee bending angle θ. Furthermore, in this embodiment, theaforementioned knee bending angle θ corresponds to a relativedisplacement amount between the thigh portion 4 and the crus portion 5as a pair of link members.

[0062] Referring back to FIG. 1, mounted within the body 2 of the robot1 are: a control unit 27 which performs, for example, operation controlof the respective joints 7, 8 and 9 of each of the legs 3; a storagedevice 28 as a power source of the electric motors of the respectivejoints 7, 8 and 9, and the like; an inclination sensor 29 which detectsan inclination angle of the body 2; a motor driver circuit 30 forcontrolling energizing of the respective electric motors; and the like.Note that the inclination sensor 29 is configured by using a gyrosensor, an accelerometer or the like. Moreover, the storage device 28 isconfigured by a battery (secondary battery), a condenser or the like.

[0063] The control unit 27 is configured by electronic circuitsincluding a microcomputer and the like. As shown in FIG. 5, the controlunit 27 is provided with a gait generator 31, a motor controller 32, anda lock mechanism controller 33 as functional constituents thereof.

[0064] In each step (every time a supporting leg changes) while therobot 1 is moving, the gait generator 31 decides gait parameters (lengthof step, walking cycle, motion mode and the like) which define desiredgaits of both legs 3 and 3 of the robot 1 (desired forms of the motionsof both legs 3 and 3), corresponding to a command from the outside,teaching data (data for a planned movement) which has been already set,or the like. Further, based on the gait parameters, the gait generator31 generates a desired gait (a desired instantaneous gait) for eachpredetermined control cycle. Here, the gait parameters generated by thegait generator 31 in this embodiment are parameters which define thedesired gaits and the like for permitting the robot 1 to perform anormal walking motion and the same for permitting the robot 1 to performa running motion similar to a human running motion. The desired gaitincludes, for example: desired values of position and posture of thebody 2 of the robot 1 (hereinafter, referred to as desired bodyposition/posture); desired values of position and posture of each of thefoot potions 6 of the robot 1 (hereinafter, referred to as desired footposition/posture); a desired value of a resultant force (total floorreaction force) of floor reaction forces (translation forces and moment)acting on the respective foot portions 6 and 6 (hereinafter, referred toas desired total floor reaction force); and a desired position ofso-called ZMP (Zero Moment Point) (hereinafter, referred to as a desiredZMP) as a point of action of the total floor reaction force. Note thatfurther details of constituents of the aforementioned desired gait areprovided by the applicant of the application concerned, in JapanesePatent Laid-Open Publication No. Heisei 11-300660, for example. Thus,detailed description thereof is omitted herein. Moreover, the content ofthe desired gait is not limited to that disclosed in the abovementionedpublication, as long as it expresses a desired form of the motion of therobot 1.

[0065] The lock mechanism controller 33 has a function to control thelock mechanism 24 of the foregoing assist device 12 to be in theaforementioned locked state or the free state. Corresponding to thedesired gait (to be more specific, the gait parameters defining thedesired gait) generated by the gait generator 31, this lock mechanismcontroller 33 decides a period during which the lock mechanism 24 is inthe locked state (this state corresponds to a second predeterminedperiod in this invention, and hereinafter referred to as a lock period)or a period during which the lock mechanism 24 is in the free state(this state corresponds to a first predetermined period in thisinvention, and hereinafter referred to as a free period) as describedlater. During the decided lock period, the lock mechanism controller 33outputs a lock command to the lock mechanism 24 in order to direct thelock mechanism 24 to the locked state. Alternatively, in the decidedfree period (a period except the lock period), the lock mechanismcontroller 33 outputs a free command to the lock mechanism 24 in orderto direct the lock mechanism 24 to the free state. Here, in thisembodiment, the lock mechanism 24 is actuated by moving the latch pin 25forward and backward by the use of the electromagnetic solenoid 26 asdescribed earlier. Therefore, to be more specific, the abovementionedlock command and the free command are commands for energization controlof the aforementioned electromagnetic solenoid 26 of the lock mechanism24. Note that the lock mechanism controller 33 corresponds to controlmeans in this invention.

[0066] The motor controller 32 sequentially controls the electric motorsof the respective joints 7, 8 and 9, including the foregoing knee jointelectric motor 10 (specifically, sequentially controls rotation anglesof the electric motors). As described later, this motor controller 32sequentially generates torque commands (specifically, command values ofthe current to energize the electric motors) which define torque to begenerated in the respective electric motors, based on the desired gaitgenerated by the gait generator 31, an actual inclination angle of thebody 2 detected by the foregoing inclination sensor 29, actual rotationangles of the respective joints 7, 8 and 9 of the leg 3 detected byusing the unillustrated encoders, an actual floor reaction force of eachof the foot portions 6 detected by the foregoing six-axis force sensor11, data of the foregoing lock period (or the free period) decided bythe foregoing lock mechanism controller 33, and the like. Thereafter,the motor controller 32 outputs the generated torque commands to themotor driver circuit 30, causing the respective electric motors togenerate torque in accordance with the torque commands, through themotor driver circuit 30.

[0067] Next, actuation of a system of this embodiment is described. Theaforementioned control unit 27 performs a predetermined initializationprocessing such as initialization of a timer and the like, andthereafter executes processing of the flowchart in FIG. 6 for eachpredetermined control cycle (for example, 50 ms) which is set inadvance. Specifically, the control unit 27 first determines whether itis a switch moment of the gait of the robot 1 (STEP 1). To be morespecific, the switch moment of the gait is the instance of thesupporting leg, one of the legs 3, switching to the other leg 3, whilethe robot 1 is moving. When the switch moment of the gait does not existin STEP 1, the processing of the control unit 27 proceeds to aprocessing in STEP 3 which will be described later.

[0068] When it is a switching moment of the gait, in STEP 1, the controlunit 27 causes the foregoing gait generator 31 to generate (renew) thegait parameters which define the desired gait of the robot 1, based on amotion command of the robot 1 given from the outside or the data for aplanned movement set in advance (STEP 2). Here, the desired gait definedby the gait parameters generated by the gait generator 31 is a desiredgait used until the next switch moment in the gait or the momentslightly after the next switch moment in the gait. Additionally, in thiscase, the desired gait defined by the gait parameters generated by thegait generator 31 is a desired gait of a running motion of the robot 1(for example, a desired gait with which the robot 1 performs motions ofthe legs 3 and 3 with steps similar to those of a running human), in acase where the motion command, indicating that the robot 1 shouldperform a running motion, is given from the outside, or in a situationwhere the robot 1 should perform a running motion according to the datafor a planned movement of the robot 1.

[0069] Next, the control unit 27 executes processings of STEPS 3 to 5 byuse of the motor controller 32. The processings of STEPS 3 to 5 are forobtaining torque commands (hereinafter, referred to as basic torquecommands) to the electric motors of the respective joints 7, 8 and 9,when the lock mechanism 24 of the assist device 12 is in the free state(where the auxiliary knee rotation force by the spring means 15 does notact on the knee joint 8). These torque commands are required in order todirect the motion of the robot 1 to follow the aforementioned desiredgait. Note that the processings of STEP 3 to 5 have already beendetailed by the applicant of the application concerned in JapanesePatent Laid-Open Publication No. Heisei 11-300660. Therefore, briefoutlines of the processings of STEP 3 to 5 are provided in thefollowing.

[0070] In STEP 3, the control unit 27 obtains a desired instantaneousgait based on the gait parameters currently generated by the gaitgenerator 31. The desired instantaneous gait is the desired gait foreach control cycle of processing of the control unit 27. To be morespecific, the desired instantaneous gait includes the desired bodyposition/posture, the desired foot position/posture, the desired totalfloor reaction force, and the desired ZMP, for each control cycle, asmentioned earlier. Note that, in the processing of STEP 3, a desiredfloor reaction force of each of the legs 3 for each control cycle aswell as a point of action of the desired floor reaction force of thesame are further obtained, based on the above-mentioned desired footposition/posture, the desired total floor reaction force, the desiredZMP and the like.

[0071] In STEP 4, the control unit 27 corrects the desired footposition/posture of the above-mentioned desired instantaneous gait by acomposite-compliance operation processing. To be more specific, in thiscomposite-compliance operation processing, obtained is a floor reactionforce (moment) to be acted on the robot 1 in order to restore the actualinclination angle of the body 2 of the robot 1 (detected by theforegoing inclination sensor 29) to a desired inclination angle set bythe aforementioned desired body position/posture (cause the deviationbetween the actual inclination angle and the desired inclination angleto be “0”). Thereafter, a resultant force of this floor reaction force(moment) and the aforementioned desired total floor reaction force isset as a desired value of the entire floor reaction force to be actuallyacted on the robot 1. Subsequently, the desired foot position/posturefor each control cycle is corrected so that a resultant force of theactual floor reaction force of each of the foot portions 6, detected bythe six-axis sensor 11 of each of the legs 3, follows the desired value.This kind of composite-compliance operation processing is for ensuringautonomous stability of the posture of the robot 1.

[0072] In STEP 5, the control unit 27 obtains the basic torque commandsto the respective electric motors of the joints 7, 8 and 9 of each ofthe legs 3 of the robot 1. To be more specific, in this processing,desired rotation angles of the respective joints 7, 8 and 9 of each ofthe legs 3 of the robot 1 are obtained by an inverse kinematicscalculation processing based on a model of the robot 1 (a rigid bodylink model), using the desired body position/posture in the desiredinstantaneous gait, the desired foot position/posture corrected in STEP4 as mentioned above, and the like. Thereafter, the torque commands tothe electric motors of the respective joints 7, 8 and 9 are obtained sothat actual rotation angles of the respective joints 7, 8 and 9(detected by the unillustrated encoder provided in each of the joints 7,8 and 9) follow these-desired rotation angles.

[0073] In this case, for example, the torque command for the knee jointelectric motor 10 of each of the legs 3 is obtained by the followingequation (1) using a deviation Δθ between the desired rotation angle ofthe knee joint 8 (desired value of the knee bending angle θ) and anactual rotation angle of the knee joint 8 (detected value of the kneebending angle θ), and torque Tff of the electric motor 10 (hereinafter,referred to as a reference torque Tff) required to generate theaforementioned desired floor reaction force to the leg 3.

Basic torque command=Kp·Δθ+Kv·(dΔθ/dt)+Tff   (1)

[0074] Note that the reference torque Tff used for the calculation ofthe equation (1) is obtained by the inverse kinematics calculationprocessing (inverse dynamics calculation processing) based on a model ofthe robot 1, using the desired body position/posture, the desired footposition/posture, the desired floor reaction force to the leg 3, desiredrotation angle acceleration of each of the joints 7, 8 and 9, and thelike. Further, factors Kp and Kv of the equation (1) are gaincoefficients set in advance. A factor dΔθ/dt is the time derivative ofthe deviation Δθ.

[0075] Here, the first and second terms on the right hand side of theequation (1) are feedback control terms corresponding to the deviationΔθ. The third term on the right hand side thereof is a feed-forwardcontrol term for compensating an influence of the floor reaction forceacting on the leg 3. The second term on the right hand side inparticular is a term having a buffer function (damping function) whichswiftly diminishes vibration relative to the desired value of the kneebending angle θ.

[0076] The basic torque commands for the electric motors of the joints 7and 9 other than the knee joint 8 are obtained in a similar manner tothe above. As described earlier, the basic torque commands obtained inthis manner are torque commands to the electric motors of the respectivejoints 7, 8 and 9, required to cause the motion of the robot 1 to followthe foregoing desired gait in a state where the auxiliary knee jointrotation force by the spring means 15 of the assist device 12 is notacting on the knee joint 8.

[0077] Next, in STEP 6, the control unit 27 causes the foregoing lockmechanism controller 33 to execute a processing for controlling the lockmechanism 24 of the assist device 12. This processing is performed asshown in the flowchart in FIG. 7. Specifically, the lock mechanismcontroller 33 first sets the lock period during which the lock mechanism24 is in the locked state, based on the gait parameters currently set bythe gait generator 31 (STEP 6-1). In this case, in the presentembodiment, when the gait parameters are those which cause the robot 1to perform, for example, a normal walking motion, the lock mechanismcontroller 33 directs the lock mechanism 24 to the free state (does notallow the auxiliary knee rotation force by the spring means 15 to act onthe knee joint 8) over the entire period of the walking motion. Hence,the lock period is not set in this case.

[0078] On the other hand, when the gait parameters are those which causethe robot 1 to perform, for example, a running motion (running motionsimilar to that of a human), the lock period is set so as to direct thelock mechanism 24 to the locked state during a predetermined period ofthe gait of the robot 1, as described below.

[0079] Prior to specific description about setting of the lock period,description is provided, with reference to FIG. 8, regarding the desiredrotation angle of the knee joint 8 (hereinafter, referred to as adesired knee bending angle) determined by the desired gait in therunning motion of the robot 1 in this embodiment, and a rotation forceto be acted on the knee joint 8 corresponding to the desired kneebending angle (hereinafter, referred to as a required knee rotationforce). An upper diagram in FIG. 8 shows how the desired knee bendingangle of the knee angle 8 of any one of the legs 3 and 3 changes withtime during the running motion of the robot 1 (the running motion withfootsteps similar to those in a normal running motion of a human). Amiddle diagram in FIG. 8 shows how the required knee rotation forcecorresponding to the desired knee bending angle in the upper diagram ofFIG. 8 changes with time. Note that a lower diagram in FIG. 8 shows howthe lock period is set, which will be described later.

[0080] When the robot 1 performs the running motion in a similar form tothat of the normal running motion of a human, the desired knee bendingangle increases (a bending degree of the leg 3 at the knee joint 8increases) during the first half of a supporting leg period during whichthe foot portion 6 of the leg 3 lands on the floor, as shown in theupper diagram in FIG. 8. During the latter half of the supporting legperiod, the desired knee bending angle decreases (the bending degree ofthe leg 3 at the knee joint 8 decreases) until the moment immediatelybefore the end of the supporting leg period. Moreover, the desired kneebending angle increases from a moment immediately before the end of thesupporting leg period through the first half of a free leg period (aperiod during which the foot portion 6 of the leg 3 is lifted off thefloor). Thereafter, during the latter half of the free leg period, thedesired knee bending angle decreases until the moment immediately beforethe end of the free leg period. Note that the desired knee bending angleslightly increases at the moment immediately before the end of the freeleg period. Thus, maximum values of the desired knee bending angle inthe running motion are observed at mid points of the supporting legperiod and the free leg period. A minimum value of the same is observedimmediately before the end of the supporting leg period.

[0081] Moreover, during the first half of the supporting leg period(generally, a period during which the desired knee bending angleincreases), the required knee rotation force (the rotation forces in thebending direction and stretching directions of the leg 3 are expressedby a positive value and a negative value, respectively) greatlydecreases from a positive rotation force to a negative rotation force(the rotation force greatly increases in the stretching direction of theleg 3). During the latter half of the supporting leg period (generally,a period during which the desired knee bending angle decreases) untilthe moment immediately before the end of the supporting leg period, therequired knee bending angle increases up to a rotation force ofapproximate “0.” From the moment immediately before the end of thesupporting leg period through the first half of the free leg period, therequired knee rotation force slowly decreases to a small negative value.Thereafter, during the latter half of the free leg period, the requiredknee rotation force slowly increases to a positive value from thenegative value. Therefore, the required knee rotation force during therunning motion increases in the stretching direction of the leg 3particularly during the supporting leg period. In addition, the requiredknee rotation force in the stretching direction becomes maximum at aboutthe mid point of the supporting leg period (this point generallycorresponds to when the knee bending angle reaches a maximum value).

[0082] In this embodiment, in consideration of the aforementionedcharacteristics of the desired knee rotation angle and the required kneerotation force during the running motion of the robot 1, the auxiliaryknee rotation force by the spring means 15 of the foregoing assistdevice 12 is acted on the knee joint 8 basically during a period withinthe supporting leg period of the leg 3, during which the required kneerotation force greatly increases in the stretching direction of the leg3. In order to cause the auxiliary knee rotation force to act on theknee joint 8 as mentioned above, the lock period of the lock mechanism24 is set in the abovementioned STEP 6-1 in the following manner or thelike.

[0083] When the gait parameters currently set by the gait generator 31are gait parameters corresponding to the running motion of the robot 1,the lock mechanism controller 33 first obtains the desired knee bendingangle during the supporting leg period of the leg 3 (specifically, dataof changes of the desired knee bending angle with time during thesupporting leg period), based on the gait parameters. Then, at about themoment immediately before the end of the supporting leg period, the lockmechanism controller 33 finds time Toff (see the upper diagram of FIG.8) at which the desired knee bending angle shows the minimum value θoffand decides the time Toff as an stopping moment of the lock period.Further, the lock mechanism controller 33 finds time Ton at which thedesired knee bending angle becomes the same value as the above-mentionedminimum value θoff at the beginning of the supporting leg period, anddecides the time Ton as a starting moment of the lock period.Accordingly, a period from the above-mentioned time Ton to the time Toff(Ton to Toff) is set as the lock period as shown in the lower diagram inFIG. 8. Note that, as shown in the lower diagram in FIG. 8, a periodother than the lock period (Ton to Toff) is the free period during whichthe lock mechanism 24 is in the free state. By setting the lock period(Ton to Toff) as above, the lock period is preferably set as a periodduring which the desired knee rotation force greatly changes in thestretching direction of the leg 3.

[0084] After setting the lock period in STEP 6-1 as above, the lockmechanism controller 33 next determines whether the current time iswithin the lock period (STEP 6-2). If the current time is within thelock period, the lock mechanism controller 33 transmits a lock commandfor directing the lock mechanism 24 to the locked state (specifically, acommand for energizing the electromagnetic solenoid 26 so as to move thelatch pin 25 of the lock mechanism 24 forward) to the lock mechanism 24(STEP 6-3). On the other hand, when the current time is not within thelock period, the lock mechanism controller 33 transmits a free commandfor directing the lock mechanism 24 to the free state (specifically, acommand for energizing the electromagnetic solenoid 26 so as to move thelatch pin 25 of the lock mechanism 24 backward) to the lock mechanism 24(STEP 6-4). Thus, the processing of STEP 6 is finished. Note that, whenthe robot 1 performs a normal walking motion, the lock mechanism 24 isin the free state for the entire period as mentioned earlier. Thus, thelock command is not transmitted to the lock mechanism 24. In thisembodiment, during the running motion of the robot 1, the lock commandis transmitted to the lock mechanism 24 in the lock period (Ton to Toff)set in the foregoing manner.

[0085] Returning to the description of the flowchart in FIG. 6, afterexecuting the lock mechanism control processing of STEP 6 as describedabove, the control unit 27 estimates the auxiliary knee rotation force(specifically, the auxiliary knee rotation force for each control cycle)by the spring means 15 of the assist device 12 (STEP 7). The estimatedvalue of the auxiliary knee rotation force is used by the motorcontroller 32 to decide a final torque command to the knee jointelectric motor 10. In this embodiment, the estimated value is obtainedby the motor controller 32, for example, in the following manner. Themotor controller 32 determines whether the lock mechanism 24 is in thelocked state or the free state. When the switch moment exists, at whichthe free state is switched to the locked state, the motor controller 32stores the current knee bending angle θ as the foregoing lock start kneebending angle. In this case, when, for example, the current time is inthe lock period set by the foregoing lock mechanism controller 33, themotor controller 32 determines that the lock mechanism 24 is in thelocked state. When the current time is not in the lock period, the motorcontroller 32 determines that the lock mechanism 24 is in the freestate. Thereafter, at the start time of the lock period (start time oftransmitting the aforementioned lock command), the motor controller 32stores the knee bending angle θ, detected by the unillustrated encoder,as the foregoing lock start knee bending angle.

[0086] Note that, in this embodiment, the recesses 16 a of the rodmember 16 of the lock mechanism 24 are discretely provided. Thus, thelocked state of the lock mechanism 24 does not always startsimultaneously with the start time of the lock period set by the lockmechanism controller 33. The lock mechanism 24 is actually directed tothe locked state when the latch pin 25 is fitted into the recess 16 athat the latch pin 25 faces first, after the start of transmission ofthe lock command from the lock mechanism controller 33. Therefore, forexample, in a case where a position of the latch pin 25 in motion isdetected by an unillustrated sensor, it is preferred that the motorcontroller 32 determine that the lock mechanism 24 is in the lockedstate when the sensor detects the latch pin 25 is moving forward, inother words, the latch pin 25 being fitted into any one of the recesses16 a of the rod member 16. In addition, it is preferred that the motorcontroller 32 store the knee bending angle θ at the start time of thelocked state thus determined, as the foregoing lock start knee bendingangle.

[0087] The knee bending angle θ stored as the lock start knee bendingangle may be, for example, data of the desired knee bending angledecided based on the gait parameters generated by the gait generator 31,or data of the knee bending angle decided based on the desired footposition/posture corrected in the foregoing composite-complianceoperation processing.

[0088] Next, the motor controller 32 estimates the auxiliary kneerotation force by the spring means 15. In this case, in the presentembodiment, data indicating the characteristics of the auxiliary kneerotation force by the spring means 15 as shown by the solid lines a andb in FIG. 4 is stored in an unillustrated memory in advance. When thelock mechanism 24 is in the locked state, the auxiliary knee rotationforce by the spring means 15 is estimated based on the lock start kneebending angle stored as mentioned above, a detected value (or a desiredvalue) of a current knee bending angle θ, and the aforementioned dataindicating the characteristics of the auxiliary knee rotation force. Forexample, referring to FIG. 4, when the lock start knee bending angle is“θ2” and the current knee bending angle θ is θk, the estimated value ofthe auxiliary knee rotation force is “Mk.” Note that, when the lockmechanism 24 is in the free state, the auxiliary knee rotation force is“0.” Further, the auxiliary knee rotation force can also be detecteddirectly by the use of a force sensor or the like.

[0089] After the auxiliary knee rotation force is estimated in STEP 7 asdescribed above, the motor controller 32 of the control unit 27 decidesfinal torque commands as ultimate torque commands to the electric motorsof the respective joints 7, 8 and 9 of the leg 3 for each control cycle(STEP 8). In this case, the final torque command to the knee jointelectric motor 10 decides an actual torque command to the knee jointelectric motor 10 by subtracting the auxiliary knee rotation forceobtained in the foregoing STEP 7 from the basic torque command (torqueto be generated to the knee joint 8 corresponding to the desired gait,on an assumption that the auxiliary knee rotation force is “0”) obtainedby the equation (1) in the foregoing STEP 5. Specifically, the finaltorque command to the knee joint electric motor 10 is generated suchthat the sum of the final torque command to the knee joint electricmotor 10 (a command value of torque to be actually generated to the kneejoint electric motor 10) and the auxiliary knee rotation force becomesthe basic torque command. Note that, for the final torque command foreach of the electric motors of each of the joints 7 and 9 other than theknee joint 8, the basic torque command is used as it is.

[0090] Next, the control unit 27 outputs the final torque commandsdecided as above to the motor driver circuit 30 (STEP 9), thus endingthe processing for each control cycle. In response to the output of thefinal torque commands, the electric motors of respective joints 7, 8 and9 are energized and controlled so that the rotation angles of theelectric motors, in other words, the rotation angles of the respectivejoints 7, 8 and 9 follow required rotation angles decided on the basisof the foregoing desired body position/posture and the desired footposition/posture (corrected in the foregoing composite-complianceoperation processing). Hence, the robot 1 moves in accordance with thedesired gait defined by the gait parameters.

[0091] In the system of this embodiment, the lock mechanism 24 isdirected to the locked state and the auxiliary knee rotation force bythe spring means 15 thus acts on the knee joint 8, only in a periodduring which the required knee rotation force becomes large in thestretching direction of the leg 3 (during a portion of the supportingleg period) while the robot 1 is in the running motion. In addition, thelocked state starts when the knee bending angle θ is relatively small.Thus, as the knee bending angle θ increases after the start of thelocked state, the auxiliary knee rotation force by the spring means 15can be increased to a sufficient level for the required knee rotationforce. Accordingly, torque to be generated to the knee joint electricmotor 10 can be relatively small during the period during which the lockmechanism 24 is in the locked state (lock period). Thus, the currentenergizing the knee joint electric motor 10 may only be relatively smallover the entire period of the running motion of the robot 1.Consequently, an energy loss can be small. In addition, in the lockperiod, in the state where the knee bending angle θ is increasing (astate of about the first half of the lock period in FIG. 8), the springmeans 15 generates an elastic force (auxiliary knee rotation force)while storing elastic energy from kinetic energy of the robot 1. In thestate where the knee bending angle θ is decreasing, the spring means 15generates the elastic force (auxiliary knee rotation force) whilereleasing the stored elastic energy. In this case, generally, an energyloss is extremely small when switching between the elastic energy of thespring means 15 and the kinetic energy of the robot 1. Therefore,utilization efficiency of the energy in the system of this embodimentcan be ensured in a favorable manner. Further, in the state where therequired auxiliary knee rotation force is relatively small, the lockmechanism 24 is directed to the free state so that the elastic force bythe spring means 15 is not generated. Thus, the torque to be generatedto the knee joint electric motor 10 is surely maintained small, thussurely avoiding a situation causing an excessive burden on the kneejoint electric motor 10.

[0092] Moreover, in this embodiment, the knee bending angles at starttime and stop time of the locked state during the running motion of therobot 1 are equal, and thus the following effects can be obtained. Sincethe knee bending angles at the start time and the stop time of thelocked state are equal to each other, the auxiliary knee rotation forceby the spring means 15 is approximately “0” not only at the start timeof the locked state but also at the stop time of the same. Therefore, adiscontinuous change of the auxiliary knee rotation force by the springmeans 15 can be avoided during a shift from the locked state to the freestate. As a result, the behavior of the robot 1 will not be jerky duringthe shift from the locked state to the free state, and a smooth motionof the robot 1 can be realized. Further, there is the following effectparticularly when the solid spring like the coiled spring 19 shown inFIG. 2(a) is used as the spring means 15. When the solid spring like thecoiled spring 19 is used as the spring means 15, free vibration of thespring means 15 easily occurs from the stop time of the locked state(switch moment to the free state) if the knee bending angles at thestart time and the stop time of the locked state are largely differentfrom each other. When the free vibration occurs, it takes time todiminish the vibration. Thus, when re-starting the locked state, it islikely that a shift to the locked state is not performed smoothly. Yet,by setting the knee bending angles at the start time and the stop timeof the locked state to be equal like this embodiment, it becomespossible to avoid the situation causing the free vibration of the springmeans 15 at the stop time of the locked state, thereby preventing theaforementioned problems. To be more specific, the shift from the freestate to the locked state is smoothly preformed, thus smoothlygenerating the auxiliary knee rotation force by the spring means 15.

[0093] Next, a second embodiment of the present invention is describedwith reference to FIG. 9. Note that the present embodiment is differentfrom the above-described first embodiment only in actuation of the robot1 during a running motion thereof. Thus, the reference numerals andfigures same as those for the first embodiment denote the sameconstituents and functional portions as those of the first embodiment,and detailed description thereof is omitted.

[0094] In the aforementioned first embodiment, description was providedregarding the case of causing the robot 1 to perform the normal runningmotion of a human (more specifically, the running motion with the bodyinclined forward). In this embodiment, for example, the robot 1 performsa running motion with similar footstep to those of a running human withthe body thereof inclined slightly backward. Therefore, in thisembodiment, the gait generator 31 of the control unit 27 generates gaitparameters, which cause the robot 1 to perform the above-mentionedrunning motion, as appropriate based on a command from the outside or amovement plan of the robot 1, decided in advance.

[0095] In this case, in the above running motion, particularly, adesired knee bending angle defined by the gait parameters generated bythe gait generator 31 of the control unit 27 is somewhat different fromthat of the foregoing first embodiment. Referring to FIG. 9, whencausing the robot 1 to perform the similar running motion to that of therunning human with the body inclined slightly backward, the desired kneebending angle changes as shown in an upper diagram in FIG. 9. In thiscase, the general tendency of the change of the desired knee bendingangle is similar to that in the foregoing first embodiment (see FIG. 8).However, a minimum value θoff of the desired knee bending angle at themoment immediately before the end of the support leg period of the leg 3is the lowest value of the desired knee bending angle. Specifically, thedesired knee bending angle becomes larger than the minimum value θoff attime other than the time Toff at which the desired knee bending anglebecomes the minimum value θoff. Note that the required knee rotationforce corresponding to the desired knee bending angle shown in the upperdiagram in FIG. 9 changes in the almost the same form as that in thefirst embodiment. However, the magnitude of the required knee rotationforce (particularly the magnitude of the required knee rotation forceduring the supporting leg period) is different from that of the firstembodiment.

[0096] In this embodiment, in consideration of the above-describedcharacteristics of the desired knee bending angle and the required kneerotation force, the lock period during which the lock mechanism 24 isdirected to the locked state is set in the following manner in theforegoing processing of STEP 6-1 in FIG. 7. When the gait parameterscurrently set by the gait generator 31 are gait parameters for causingthe robot 1 to perform the running motion corresponding to that of therunning human with the body inclined slightly backward, the lockmechanism controller 33 of the control unit 27 first obtains the desiredknee bending angles in the supporting leg period and the free leg period(specifically, data of changes of the desired knee bending angles withtime during the supporting leg period and the free leg period), based onthe gait parameters. The lock mechanism controller 33 then decides thetime Toff (see the upper diagram in FIG. 9), at which the desired kneebending angle becomes the minimum value θoff at about a momentimmediately before the end of the supporting leg period, as the stoppingmoment of the lock period. This process of deciding the stopping momentof the lock period is the same as that of the first embodiment.Additionally, the lock mechanism controller 33 finds time Tc at whichthe desired knee bending angle becomes a minimum value θc at a momentimmediately before the end of the free leg period (see the upper diagramin FIG. 9), and decides the time Tc as the start moment of the lockperiod. Thus, as shown in a lower diagram in FIG. 9, a period from thetime Toff to the time Tc (Toff to Tc) is set as the free period, and aperiod other than the free period is set as the lock period.Accordingly, the lock period is set as a period during which therequired knee rotation force is greatly changed in the stretchingdirection of the leg 3.

[0097] The actuation other than the above described actuation is thesame as that in the foregoing first embodiment. In this embodiment, aneffect similar to that of the first embodiment can be achieved. In thiscase, however, the knee bending angle θc at the start time of the lockedstate (a lock start knee bending angle) and the knee bending angle θoffat the stop time of the lock period are not the same. Nevertheless, thedifference between these angles is relatively small. Therefore, there isno problem in practical use. In addition, by using a gas spring (forexample, the spring with the configuration shown in FIG. 2(b)) as thespring means 15, free vibration of the spring means 15 at the stop timeof the locked state can be avoided from being generated (generally, thefree vibration hardly occurs in the gas spring).

[0098] Note that, in the first and second embodiments described so far,the lock period and the free period are set in the above mentionedmanner. However, the manner for setting those periods is not limited tothe above. For example, the starting or the stopping moment of the lockperiod may be set as a predetermined time before or after the footlanding time of the leg 3, or as a predetermined time before or afterthe foot of the leg 3 is lifted off the floor. Alternatively, thestarting or stopping moment of the lock period may be set as a timepoint at which the knee bending angle or the rate of change (angularvelocity) thereof reaches a predetermined value. In addition, thestopping moment of the lock period in particular may be a time point atwhich (the detected or desired value of) the knee bending angle θbecomes the knee bending angle at the start time of the lock period(lock start knee bending angle) or lower, after the start of the lockperiod. Alternatively, the stopping moment of the lock period may be atime point at which the absolute value of (the detected or estimatedvalue of) the auxiliary knee rotation force by the spring means 15becomes a predetermined value or lower (approximately “0”). Basically,it is preferred that the lock period be set as a period during which theknee bending angles at the start time and the stop time thereof arealmost the same, and the required knee rotation force greatly increasesin the stretching direction of the leg 3.

[0099] Moreover, in the first and second embodiments, the lock mechanism24 is directed to the locked state by the fit between the latch pin 25of the lock mechanism 24 and the recess 16 a of the rod member 16.However, the lock mechanism 24 may be directed to the locked state by,for example, releasably cramping the rod member 16 by a frictionalforce. In this case, the lock mechanism can be directed to the lockedstate at an arbitrary knee bending angle. Further, in this case, freevibration of the spring means 15 may be suppressed by, for example,gradually decreasing the frictional force for cramping the rod member16, at the stop moment of the locked state. Note that a technique ofcramping the rod member 16 by the frictional force as above can besimilarly applied to third and fourth embodiments described below.

[0100] Next, the third embodiment of the present invention is describedwith reference to FIGS. 10(a), 10(b) and 11. Note that this embodimentis different from the abovementioned first and second embodiments onlyin the configuration of the lock mechanism (motion transmissioncontinuation/discontinuation means) of the assist device. Thus, thereference numerals and figures same as those for the first embodimentdenote the same constituents and functional portions as those of thefirst embodiment, and description thereof is omitted.

[0101] Referring to FIG. 10(a), in the lock mechanism 34 of the assistdevice 12 of this embodiment, the upper portion of the rod member 16connected to the spring means 15 (see FIG. 1) is inserted through athrough hole 36 in a rod insertion member 35. In this case, the upperend of the through hole 36 is closed. A locking rod member 37 and aspring 38 are accommodated within the through hole 36 between the upperend of the through hole 36 and the upper end face of the rod member 16.The locking rod member 37 is movable in the axis direction of the rodmember 16 (the axis direction of the through hole 36) and the spring 38biases the locking rod member 37 downward so as to contact the lockingrod member 37 against the upper end face of the rod member 16. Aplurality of recesses 37 a is provided on the side portion of thelocking rod member 37 at intervals in the axis direction of the lockingrod member 37. In addition, similarly to the lock mechanism 24 of theforegoing first and second embodiments, the latch pin 25 can be fittedinto each of these recesses 37 a. The latch pin 25 is moved forward andbackward by energization control of the electromagnetic solenoid 26.Note that, similarly to the rod insertion member 17 of the foregoingfirst and second embodiments, the circumference portion of the rodinsertion member 35 is connected to the thigh portion 4 of each of thelegs 3 through the free joint 18 (see FIG. 1). The configurations otherthan the above-mentioned configuration are the same as those of theaforementioned first and second embodiments.

[0102] In the lock mechanism 34 having the above configuration, the freestate thereof is a state where the latch pin 25 is moved backward and isnot fitted into any of the recesses 37 a as shown in FIG. 10(a). In thisfree state, the rod member 16 can be freely moved integrally with thelocking rod member 37 in the knee bending and stretching motion of theleg 3. In this case, the biasing force of the above-mentioned spring 38is sufficiently small and thus the spring means 15 is kept in the almostnatural length state. Therefore, the auxiliary knee rotation force bythe spring means 15 does not substantially act on the knee joint 8.

[0103] Further, the locked state of the lock mechanism 34 is a statewhere the latch pin 25 is fitted into one of the recesses 37 a of thelocking rod member 37 as shown in FIG. 10(b). In this locked state, oncethe knee bending angle becomes larger than the knee bending angle at thestart time of the locked state (lock start knee bending angle) (a stateof the bending motion of the leg 3 at the knee joint 8), the springmeans 15 stores elastic energy and generates an elastic force. Thiselastic force acts on the knee joint 8 in the stretching direction ofthe leg 8. On the other hand, when the knee bending angle becomessmaller than the above-mentioned lock start knee bending angle (a stateof the stretching motion of the leg 3 at the knee joint 8), the rodmember 16 is separated from the locking rod member 37 as shown in FIG.10(b) and the spring means 15 is kept in the almost natural lengthstate. Thus, the auxiliary knee rotation force by the spring means 15stops acting on the knee joint 8.

[0104] Therefore, when the lock mechanism 34 is directed to the lockedstate, the auxiliary knee rotation force generated by the spring means15 exhibits the characteristics shown by, for example, a solid line c ord in FIG. 11, relative to the knee bending angle θ. Here, θ3 and θ4 inFIG. 11 denote the lock start knee bending angles. As described above,in the assist device 12 provided with the lock mechanism 34 of thisembodiment, the auxiliary knee rotation force is not generated in thebending direction of the leg 3 at the knee joint 8. The auxiliary kneerotation force is generated in the stretching direction of the leg 3only when the knee bending angle θ is larger than the lock start kneebending angles θ3 and θ4.

[0105] In the system of this embodiment provided with theabove-mentioned lock mechanism 34, control processing is executed by thecontrol unit 27 similarly to the foregoing first and second embodiments.In this case, even if, for example, the lock period is erroneously setby the lock mechanism controller 33 of the control unit 27 during therunning motion of the robot 1, the auxiliary knee rotation force is notgenerated by the spring means 15 in the bending direction of the leg 3,in a state where the auxiliary knee rotation force by the spring means15 is not required. Therefore, it is possible to avoid a situation wherethe burden on the knee joint electric motor 10 ends up being large.Moreover, even when the locked state of the lock mechanism 34 is startedduring the stretching motion of the leg 3 at the knee joint 8, theauxiliary knee rotation force by the spring means 15 is not generatedduring the stretching motion. Thus, it is possible to start the lockperiod while the knee bending angle θ is decreasing, for example, in thelatter half of the free leg period of the leg 3.

[0106] Next, a fourth embodiment of the present invention is describedwith reference to FIGS. 12(a) and 12(b). Note that this embodiment isdifferent from the foregoing first and second embodiments only in theconfiguration of the lock mechanism (motion transmissioncontinuation/discontinuation means) of the assist device 12. Thus, thereference numerals and figures same as those for the first embodimentdenote the same constituents and functional portions as those of thefirst embodiment, and description thereof is omitted.

[0107] Referring to FIG. 12(a), in a lock mechanism 39 of the assistdevice 12 of this embodiment, a shape of each recess 16 a′ provided inthe rod member 16 is different from that in the foregoing first andsecond embodiments. Specifically, in this embodiment, a tapered surface16 b, inclined from the upper end side of each of the recesses 16 a′ tothe lower end side of the same, is formed in the bottom surface of eachof the recesses 16 a′ in the rod member 16. This tapered surface 16 b isformed so that the depth of each of the recesses 16 a′ graduallyincreases from the upper end side to the lower end side thereof. Inaddition, the end portion of the latch pin 25 is formed to have asimilar shape to that of each of the above-mentioned recesses 16 a′ andcan be fitted into each of the recesses 16 a′. The configurations otherthan the above-mentioned configuration are absolutely the same as thoseof the foregoing first and second embodiments. Further, controlprocessing by the control unit 27 is the same as that of the foregoingfirst and second embodiments.

[0108] In the system of this embodiment, in which the above lockmechanism 39 is provided in the assist device 12, the free state of thelock mechanism 39 is a state where the latch pin 25 is moved backwardand withdrawn from the recess 16 a′ of the rod member 16 (a state ofFIG. 12(a)). The actuation of the assist device 12 in the free state isabsolutely the same as that of the first and second embodiments.

[0109] Further, as shown in FIG. 12(b), the locked state of the lockmechanism 39 is a state where the latch pin 25 is moved forward andfitted into one of the recesses 16 a′ of the rod member 16. In thislocked state, the actuation of the assist device 12 is similar to thatof the foregoing third embodiment. Specifically, when the knee bendingangle becomes larger than the knee bending angle at the start time ofthe locked state (lock start knee bending angle), the spring means 15stores elastic energy and generates an elastic force. This elastic forcethen acts on the knee joint 8 in the stretching direction of the leg 3.Moreover, when the knee bending angle becomes smaller than the lockstart knee bending angle, the latch pin 25 is withdrawn from the recess16 a′, since each of the recesses 16 a′ has the aforementioned taperedsurface 16 b. Thereafter, the rod member 16 moves as shown by an arrowin FIG. 12(b). Therefore, the spring means 15 is kept in the almostnatural length state, and thus the auxiliary knee rotation force by thespring means 15 stops acting on the knee joint 8.

[0110] Accordingly, when the lock mechanism 39 is directed to the lockedstate, the auxiliary knee rotation force generated by the spring means15 has the foregoing characteristics shown in FIG. 11, relative to theknee bending angle θ, similarly to the foregoing third embodiment.Specifically, in this embodiment, the auxiliary knee rotation force isnot generated either in the bending direction of the leg 3 at the kneejoint 8, similarly to the foregoing third embodiment. Thus, a similareffect to that of the foregoing third embodiment can be achieved.

[0111] Note that, in the assist device 12 of this embodiment, in a casewhere the lock period (more precisely, transmission of the lock commandto the lock mechanism 39) is started while the knee bending angle θ isdecreasing during, for example, the latter half of the free leg periodof the leg 3 during the running motion of the robot 1, the substantiallocked state of the lock mechanism 39 starts in a process where the kneebending angle θ increases from the moment immediately before the end ofthe free leg period of the leg 3 (same for the assist device 12 of theforegoing third embodiment). In this case, especially in the lockmechanism 39 of this embodiment, basically, the substantial locked statestarts when the latch pin 25 of the lock mechanism 39 is fitted into therecess 16 a′ at the knee bending angle smaller than that at the timepoint at which transmission of the lock command is started (when thelatch pin 25 is fitted into a lower recess 16 a of the rod member 16).For example, referring to FIG. 11, if the lock command is transmittedwhen the knee bending angle θ is “θ3” during the stretching motion ofthe leg 3 in the latter half of the free leg period of the leg 3, thesubstantial locked state of the lock mechanism 39 starts later, forexample, when the knee bending angle θ is “θ4” (θ4<θ3). In other words,the substantial locked state of the lock mechanism 39 can be started ina state where the knee bending angle θ becomes smallest possible valuewhen the free leg period of the leg 3 shifts to the supporting legperiod of the same. Thus, the auxiliary knee rotation force generated bythe spring means 15 can be relatively large in the supporting legperiod, thereby reducing the burden on the knee joint electric motor 10more effectively.

[0112] Next, a fifth embodiment of the present invention is describedwith reference to FIG. 13. Note that this embodiment is different fromthe first and second embodiments only in the mechanical configuration ofthe assist device (especially, the mechanism of the motion transmissioncontinuation/discontinuation means). Thus, the reference numerals andfigures same as those for the first embodiment denote the sameconstituents and functional portions as those of the first embodiment,and description thereof is omitted.

[0113] Referring to FIG. 13, an assist device 40 of this embodiment isprovided with the rod member 14 connected to the crus portion 5 of eachof the legs 3 through the free joint 13, and the rod member 16 connectedto the rod member 14 through the spring means 15, similarly to theassist device of the foregoing first and second embodiments. Inaddition, in this embodiment, one end potion of a connecting member 42is connected to the upper end portion of the rod member 16 through afree joint 41. The other end of the connecting member 42 is releasablyconnected to the thigh portion 4 through a crutch mechanism 43 (whichcorresponds to the lock mechanism in the first and second embodiments)serving as the motion transmission continuation/discontinuation means.The clutch mechanism 43 fixes the connecting member 42 to the thighportion 4 and releases the-fixed connecting mechanism 42. The clutchmechanism 43 is configured by, for example, an electromagnetic clutch.The configurations other than the above-described configuration are thesame as those of the foregoing first and second embodiments. Inaddition, control processing by the control unit 27 is the same as thatof the first and second embodiments. Note that, in this case, the clutchmechanism 43 fixes the connecting member 42 to the thigh portion 4 inaccordance with the lock command transmitted from the lock mechanismcontroller 33 of the control unit 27, and the connecting member 42 fixedto the thigh portion 4 is released in accordance with the free command,in this embodiment.

[0114] In the assist device 40 of this embodiment, a state where theconnecting member 42 is fixed to the thigh portion 4 by the clutchmechanism 43 corresponds to the foregoing locked state. In this lockedstate, the spring means 15 generates an elastic force (auxiliary kneerotation force) corresponding to the knee bending and stretching motion.Further, a state where the connecting member 42 fixed to the thighportion 4 is released by the clutch mechanism 43 corresponds to theforegoing free state. In this free state, the knee bending andstretching motion is not transmitted to the spring means 15 and thus thespring means 15 does not generate the elastic force (auxiliary kneerotation force). Therefore, an effect of action similar to those of theforegoing first and second embodiments can be achieved.

[0115] Next, a sixth embodiment of the present invention is describedwith reference to FIGS. 14 and 15. Note that this embodiment isdifferent from the foregoing first and second embodiments only in themechanical configuration of the assist device (especially the mechanismof the motion transmission continuation/discontinuation means). Thus,the reference numerals and figures same as those for the firstembodiment denote the same constituents and functional portions as thoseof the first embodiment, and description thereof is omitted.

[0116] Referring to FIG. 14, an assist device 44 of this embodiment isprovided with the rod members 14 and 16 connected to each other throughthe spring means 15, similarly to the assist devices of the first andsecond embodiments. In this case, the lower end portion of the rodmember 14 on the lower side is connected to one end portion of aconnecting member 46 through a free joint 45. The other end potion ofthe connecting member 46 is releasably connected to the crus portion 5through a clutch mechanism 47 (the motion transmissioncontinuation/discontinuation means) in the area of the knee joint 8 ofeach of the legs 3. Moreover, the upper end portion of the rod member 16on the upper side is connected to the thigh portion 4 through a freejoint 48.

[0117] Here, a connecting structure of the connecting member 46 and thecrus portion 5 is more specifically described with reference to FIG. 15.The crus potion 5 is provided with a rotating shaft portion 49 along arotation axis C of the knee joint 8. The rotating shaft portion 49 isrotatably supported by the thigh portion 4 through a bearing 50. Theconnecting member 46 is releasably connected to an end of the rotatingshaft portion 49, projecting to the outside of the thigh portion 4,through the clutch mechanism 47 as illustrated. In this case, the clutchmechanism 47 fixes the connecting member 46 to the rotating shaftportion 49 of the crus portion 5 and releases the fixed connectingmember 46 therefrom. The clutch mechanism 47 is configured by anelectromagnetic clutch or the like. Note that the other end of therotating shaft portion 49 is connected to the knee joint electric motor10.

[0118] The configurations other than the above-described configurationare the same as those of the foregoing first and second embodiments. Inaddition, control processing by the control unit 27 is the same as thatof the foregoing first and second embodiments. In this case, the clutchmechanism 47 fixes the connecting member 46 to the rotating shaftportion 49 of the crus portion 5 in accordance with the lock commandtransmitted from the lock mechanism controller 33 of the control unit27, and the connecting member 46 fixed to the rotating shaft portion 49is released in accordance with the free command, in this embodiment.

[0119] In the assist device 44 of this embodiment, a state where theconnecting member 46 is fixed by the clutch mechanism 47 to the rotatingshaft portion 49 of the crus portion 5 corresponds to the foregoinglocked state. In this locked state, the spring means 15 generates anelastic force (auxiliary knee rotation force) corresponding to the kneebending and stretching motion. In addition, a state where the connectingmember 46 fixed to the rotating shaft portion 49 is released by theclutch mechanism 47 (a state where the transmission of rotation from therotating shaft portion 49 to the connecting member 46 is discontinued)corresponds to the foregoing free state. In this free state, the kneebending and stretching motion is not transmitted to the spring means 15,and thus the spring means 15 does not generate the elastic force(auxiliary knee rotation force). Therefore, an effect of action similarto those of the foregoing first and second embodiments can be achieved.

[0120] Note that, in the assist device 44 of this embodiment, theconnecting member 46 is connected to the rotating shaft portion 49 ofthe crus portion 5 through the clutch mechanism 47 in the area of theknee joint 8. Therefore, in the free state of the clutch mechanism 47, avertical movement or the like of the spring means 15 hardly occursduring the knee bending and stretching motion. Thus, particularly in thecase where the spring means 15 is configured by a coiled spring or thelike, it is possible to avoid a situation where free vibration of thespring means 15 is caused by an inertial force in the free state of theclutch mechanism 47. Accordingly, the auxiliary knee rotation force canbe smoothly generated by the spring means 15 in a shift from the freestate to the locked state.

[0121] Next, a seventh embodiment of the present invention is describedwith reference to FIGS. 16 and 17. Note that this embodiment isdifferent from the foregoing first and second embodiments only in themechanical configuration of the assist device (especially the mechanismof the motion transmission continuation/discontinuation means). Thus,reference numerals and figures the same as those for the firstembodiment denote constituents and functional portions the same as thoseof the first embodiment, and a description thereof is omitted.

[0122] Referring to FIG. 16, an assist device 51 of this embodiment isprovided with, for example, a coiled spring 52 serving as the springmeans 15. In this case, one end of the coiled spring 52 is joined withthe thigh portion 4. The other end is joined with the circumferentialportion of a pulley 53 through a wire 54. The pulley 53 is rotatablyprovided to be concentric with the rotation axis of the knee joint 8. Inaddition, a rotating shaft portion 53 a of the pulley 53 is connected tothe crus portion 5 through a clutch mechanism 55 (the motiontransmission continuation/discontinuation means) and a speed reducer 56.

[0123] Here, the connecting structure of the pulley 53 and the crusportion 5 is more specifically described with reference to FIG. 17.Similar to the case of the aforementioned sixth embodiment, the rotatingshaft portion 49 of the crus portion 5 is rotatably supported by thethigh portion 4 through the bearing 50. One end portion of the rotatingshaft portion 49, projecting to the outside of the thigh portion 4, isconnected to the output side of the speed reducer 56. The input shaft 56a of the speed reducer 56 is releasably connected to the rotating shaftportion 53 a of the pulley 53 through the clutch mechanism 55. In thiscase, the clutch mechanism 55 fixes the rotating shaft portion 53 a ofthe pulley 53 to the input shaft 56 a of the speed reducer 56 andreleases the fixed rotating shaft portion 53 a. The clutch mechanism 55is configured by an electromagnetic clutch or the like. During the kneebending and stretching motion, the speed reducer 56 increases therotation speed of the input shaft 56 a thereof so that the rotationspeed thereof becomes faster than the rotation speed of the rotationshaft portion 49 of the crus portion 5. Note that, instead of providingthe speed reducer 56 as above, the rotation of the electric motor 10 maybe transmitted to the crus portion 5 after the speed of the rotation isreduced by a speed reducer, and then transmitted to the pulley 53 as itis through the clutch mechanism 55.

[0124] The configurations other than the above-described configurationare the same as those of the foregoing first and second embodiments. Inaddition, control processing by the control unit 27 is the same as thatof the first and second embodiments. In this case, in this embodiment,the clutch mechanism 55 fixes the rotating shaft portion 53 a of thepulley 53 to the output shaft 56 a of the speed reducer 56 in accordancewith the lock command transmitted from the lock mechanism controller 33of the control unit 27. The fixed rotating shaft portion 53 a isreleased in accordance with the free command.

[0125] In the assist device 51 of this embodiment, a state where theclutch mechanism 55 fixes the rotating shaft portion 53 a of the pulley53 to the input shaft 56 a of the speed reducer 56, corresponds to theforegoing locked state. In this locked state, the coiled spring 52expands and contracts in accordance with the knee bending and stretchingmotion and generates an elastic force (auxiliary knee rotation force).Further, a state where the rotating shaft portion 53 a of the pulley 53fixed to the input shaft 56 a of the speed reducer 56 is released by theclutch mechanism 55 (a state where transmission of the rotation from theinput shaft 56 a of the speed reducer 56 to the pulley 53 isdiscontinued) corresponds to the foregoing free state. In this freestate, the knee bending and stretching motion is not transmitted to thecoiled spring 52, and thus the coiled spring 52 does not generate theelastic force (auxiliary knee rotation force). Accordingly, an effect ofaction similar to those of the foregoing first and second embodimentscan be achieved.

[0126] In this case, in the assist device 44 of this embodiment, theexpansion and contraction of the coiled spring 52 with respect tochanges in the knee bending angle θ is relatively large in the lockedstate of the clutch mechanism 55. Therefore, a relatively largeauxiliary knee rotation force can be generated by the coiled spring 52when the clutch mechanism 55 is in the locked state, thereby reducingthe burden on the knee joint electric motor 10. Thus, the assist device44 having the configuration of this embodiment is advantageous whenemploying the above-mentioned coiled spring 52 or the like withrelatively large expansion and contraction, as the spring means.

[0127] Next, an eighth embodiment of the present invention is describedwith reference to FIGS. 18 and 19. Note that this embodiment isdifferent from the foregoing first and second embodiments only in themechanical configuration of the assist device. Thus, reference numeralsand figures the same as those for the first embodiment denoteconstituents and functional portions the same as those of the firstembodiment, and a description thereof is omitted.

[0128] Referring to FIG. 18, an assist device 57 of this embodiment isprovided with a cylinder 58 formed within the thigh portion 4 of each ofthe legs 3, and a cam 59 provided at the knee joint 8 of each of thelegs 3. A piston 58 a, slidable in the axis direction of the cylinder58, is accommodated in the cylinder 58 within the thigh portion 4. Gassuch as air is sealed above and below the piston 58 a. Thus, springmeans 60 (gas spring) is configured within the cylinder 58.

[0129] The cam 59 is for moving the above-mentioned piston 58 a, and isconnected to the crus portion 5 through a clutch mechanism 61 as shownin FIG. 19. Specifically, the rotating shaft portion 49 of the crusportion 5 is rotatably supported by the thigh portion 4 through thebearing 50, similarly to the case of the foregoing sixth embodiment. Inaddition, one end of the rotating shaft portion 49, projecting to theoutside of the thigh portion 4, is releasably connected to the cam 59through the clutch mechanism 61. The clutch mechanism 61 fixes the cam59 to the rotating shaft portion 49 of the crus portion 5 and releasesthe fixed cam 59. The clutch mechanism 61 is configured by anelectromagnetic clutch or the like.

[0130] Moreover, a roller 62 is in contact with the circumferentialsurface (cam surface) of the cam 59. A rod 63 rotatably supporting theroller 62 is inserted into an insertion hole 64 of the thigh portion 4in a direction of crossing the thigh portion 4 from the side surfacethereof. In this case, the insertion hole 64 of the thigh portion 4 isformed to have a kerf shape, extending in the movable direction of theaforementioned piston 58 a (the axis direction of the cylinder 58). Asthe cam 59 rotates (as the rotating shaft portion 49 of the crus portion5 rotates about the axis C), the rod 63 is guided into the insertionhole 64 and, at the same time, moves together with the roller 62 in theaxis direction of the cylinder 58. The end portion of the aforementionedrod 63 in the insertion hole 64 is connected to a piston rod 58 bextending downward from the piston 58 a in the axis direction of thecylinder 58.

[0131] In the assist device 57 of this embodiment, a state where theclutch mechanism 61 fixes the cam 59 to the rotating shaft portion 49 ofthe crus portion 5, corresponds to the foregoing locked state. In thislocked state, the cam 59 rotates about the axis of the rotating shaftportion 49 of the crus portion 5 in accordance with the knee bending andstretching motion, and thereby the piston 58 a moves in the axisdirection of the cylinder 58 through the roller 62, the rod 63 and thepiston rod 58 b. Thus, an elastic force of the spring means 60, which isthe gas spring, is generated, and acts on the knee joint 8 as theauxiliary knee rotation force. Further, a state where the cam 59 fixedto the rotating shaft portion 49 is released by the clutch mechanism 61,corresponds to the foregoing free state. In this free state, since thecam 59 does not rotate, the piston 58 a does not move. Specifically, theknee bending and stretching motion is not transmitted to the springmeans 60, and the spring means 60 does not generate the elastic force(auxiliary knee rotation force). Therefore, an effect of action similarto those of the foregoing first and second embodiments can be achieved.Note that, in the assist device 57 having the configuration of thisembodiment, it becomes relatively easy to provide the spring means 60within the thigh portion 4, thus the entire structure of the robot 1 canbe miniaturized. Alternatively, a linear motion to rotary motiontransformer such as a crankshaft may be used instead of the cam 59.

[0132] Note that, in the fifth to eighth embodiments, when the kneebending angle θ becomes smaller than the lock start knee bending angle,the spring means can be maintained in the natural length state similarlyto the case of the third or the fourth embodiment by using, for example,the one-way clutch mechanism as each of the clutch mechanisms 43, 47, 55and 61.

[0133] Next, a ninth embodiment of the present invention is describedwith reference to FIG. 20. Note that this embodiment is different fromthe foregoing first and second embodiments only in the mechanicalconfiguration of the assist device. Thus, reference numerals and figuresthe same as those for the first embodiment denote constituents andfunctional portions the same as those of the first embodiment, and adescription thereof is omitted.

[0134] Referring to FIG. 20, an assist device 65 of this embodimentincludes a cylinder 66 provided by being connected to the thigh portion4 and the crus portion 5 outside of each of the legs 3, a cylinder 67formed within the thigh portion 4, spring means 68 accommodated withinthe cylinder 67, and a reserve tank 69 storing hydraulic oil X. Aconnecting member 71 is fixed to the bottom part of an outer cylinder 70of the cylinder 66 outside of the leg 3. The connecting member 71 isconnected to the crus portion 5 through a free joint 72. Further, apiston rod 74 extends from a piston 73 toward the upper side of theouter cylinder 70. The piston 73 is slidable within the outer cylinder70 of the cylinder 66 in the axis direction of the outer cylinder 70.The end potion (upper end portion) of the piston rod 74 is connected tothe thigh portion 4 through a free joint 75. A space 76 formed under thepiston 73 within the outer cylinder 70 is an oil chamber 76 filled withthe hydraulic oil X. Note that a space above the piston 73 within theouter cylinder 70 is opened to, for example, the atmosphere.

[0135] A piston 77, slidable in the longitudinal direction of the thighportion 4 (a vertical direction in the figure), is provided within thecylinder 67 of the thigh portion 4. The spring means 68 is placedbetween this piston 77 and the upper end portion of the inner wall ofthe cylinder 67. The spring means 68 is, for example, a solid springsuch as a coiled spring. A space 78 under the piston 77 within thecylinder 67 is an oil chamber 78 filled with the hydraulic oil X. Inthis case, the oil chamber 78 within the cylinder 67 communicates withthe oil chamber 76 of the cylinder 66 outside the leg 3 through acommunicating pipe 79, and is also connected to the reserve tank 69through a communicating pipe 80 and a switch valve 81. Here, the switchvalve 81 is an electromagnetic switch valve which can switch between aclose state and an open state. In the close state, the reserve tank 69and the oil chamber 78 of the cylinder 67 are blocked. In the openstate, the reserve tank 69 and the oil chamber 78 are opened. The switchvalve 81 corresponds to the motion transmissioncontinuation/discontinuation means in the present invention. Note thatthe reserve tank 69 and the switch valve 81 are accommodated in the body2 of the robot 1. Further, a check valve 82 shown by an imaginary linein FIG. 20 is related to a modified aspect of this embodiment, whichwill be described later.

[0136] In the assist device 65 having the above configuration, a statewhere the switch valve 81 is actuated to the open state and a statewhere the switch valve is actuated to the close state, correspond to thefree state and the locked state in the foregoing first and secondembodiments, respectively. Specifically, in the state where the switchvalve 81 is actuated to the open state, the hydraulic oil X is sent andreceived between the oil chamber 76 and the reserve tank 69 through theoil chamber 78 of the cylinder 67 within the thigh portion 4, inaccordance with changes in the volume of the oil chamber 76 of thecylinder 66 accompanying the knee bending and stretching motion of theleg 3. At this time, the pressure of the hydraulic oil X is steadily andconstantly maintained, without causing a change in the volume of the oilchamber 78 of the cylinder 67. Therefore, the spring means 68 within thecylinder 67 is maintained in the natural length state and thus does notgenerate elastic force. Thus, the elastic force by the spring means 68does not act on the knee joint 8. Accordingly, the open state of theswitch valve 81 corresponds to the free state.

[0137] On the other hand, in the state where the switch valve 81 isactuated to the close state, the hydraulic oil X is sent and receivedbetween the oil chamber 76 and the oil chamber 78 of the cylinder 67, inaccordance with changes in the volume of the oil chamber 76 of thecylinder 66 accompanying the knee bending and stretching motion of theleg 3. Thus, the piston 77 within the cylinder 67 slides and thus theelastic force of the spring means 68 is generated. Specifically, theknee bending and stretching motion of the leg 3 is transmitted to thespring means 68 through the cylinder 66 and the hydraulic oil X, and theelastic force of the spring means 68 is generated. Thereafter, theelastic force causes pressure changes in the hydraulic oil X and acts onthe knee joint 8 of the leg 3 as the auxiliary knee rotation force,through the hydraulic oil X and the cylinder 66. Accordingly, the closestate of the switch valve 81 corresponds to the locked state.

[0138] Configurations other than the above-described configuration arethe same as those of the foregoing first and second embodiments. Inaddition, control processing by the control unit 27 is the same as thatof the foregoing first and second embodiments. However, in this case,the lock command transmitted from the lock mechanism controller 33 ofthe control unit 27 is a command to cause the switch valve 81 to be inthe close state, and the free command is a command to cause the switchvalve 81 to be in the open state. Therefore, the system of thisembodiment can achieve an effect of action similar to those of theforegoing first and second embodiments. Note that the spring means 68within the cylinder 67 may be a gas spring instead of a solid springsuch as a coiled spring. In this case, gas such as air may be sealed inthe space above the piston 77. In this case, the piston 77 may beomitted so that the gas serving as the spring means is directly incontact with the hydraulic oil X within the cylinder 67. Alternatively,similar to a general accumulator for hydraulic equipment, the gas may besealed in a rubber bag and the bag is allowed to be in contact with thehydraulic oil X.

[0139] Moreover, in this embodiment, as shown by the imaginary line inFIG. 20, the check valve 82 may be connected in parallel to the switchvalve 81. In the case where the check valve 82 is provided as above,when the knee bending angle θ becomes smaller than the knee bendingangle at the start time of the locked state (lock start knee bendingangle) in the locked state in which the switch valve 81 is directed tothe close state, the hydraulic oil X flows from the reserve tank 69 tothe oil chamber 76 of the cylinder 66 similarly to the case of the freestate. Therefore, the elastic force of the spring means 68 is notgenerated. Accordingly, an effect of action similar to those in thecases of the foregoing third and fourth embodiments can be achieved.

[0140] Next, a tenth embodiment of the present invention is describedwith reference to FIG. 21. Note that this embodiment is different fromthe foregoing first and second embodiments only in the mechanicalconfiguration of the assist device. Thus, reference numerals and figuresthe same as those for the first embodiment denote constituents andfunctional portions the same as those of the first embodiment, and adescription thereof is omitted.

[0141] As shown in FIG. 21, in an assist device 83 of this embodiment, agas spring having a cylinder structure is provided as spring means 84.In this case, a connecting member 86 is fixed to the bottom portion of acylinder (outer cylinder) 85. This connecting member 86 is connected tothe crus portion 5 through a free joint 87. In addition, a piston rod 89extends toward the upper side of the cylinder 85 from a piston 88 whichis slidable within the cylinder 85 in the axis direction thereof. Theend portion (upper end portion) of this piston rod 89 is connected tothe thigh portion 4 through a free joint 90. Pressurized gas (air or thelike) is filled in gas chambers 91 and 92 formed above and under thepiston 88, respectively, within the cylinder 85. Further, these gaschambers 91 and 92 are connected to each other through a communicatingpipe 94 having a switch valve 93. Here, the switch valve 93 is anelectromagnetic switch valve which can switch between a close state andan open state. In the close state, communications between the gaschambers 91 and 92 are blocked. In the open state, these chambers areallowed to communicate with each other. The switch valve 93 correspondsto the motion transmission continuation/discontinuation means of thepresent invention.

[0142] In the assist device 83 having the above configuration, a statewhere the switch valve 93 is actuated to the open state and a statewhere the switch valve 93 is actuated to the close state correspond tothe free state and the locked state in the foregoing first and secondembodiments, respectively, similarly to the aforementioned ninthembodiment. Specifically, in the state where the switch valve 93 isactuated to the open state, the gas merely flows between theaforementioned gas chambers 91 and 92 in accordance with a movement ofthe piston 88 accompanying the knee bending and stretching motion of theleg 3. Thus, the spring means 84 does not generate the elastic force,and the elastic force by the spring means 84 does not act on the kneejoint 8.

[0143] Further, in the state where the switch valve 93 is actuated tothe close state, the gas in one of the gas chambers 91 and 92 iscompressed and the gas in the other gas chamber is expanded due to themovement of the piston 88 at the same time accompanying the knee bendingand stretching motion of the leg 3. Thus, the elastic force by thespring means 84 is generated. This elastic force then acts on the kneejoint 8 of the leg 3 as the auxiliary knee rotation force.

[0144] The configurations other than the above-described configurationare the same as those of the foregoing first and second embodiments. Inaddition, control processing by the control unit 27 is the same as thatof the foregoing first and second embodiments. In this case, however,the lock command transmitted by the lock mechanism controller 33 of thecontrol unit 27 is a command directing the switch valve 93 to the closestate, and the free command is a command directing the switch valve 93to the open state, similarly to the case of the aforementioned ninthembodiment. Therefore, the system of this embodiment can achieve aneffect of action similar to those of the foregoing first and secondembodiments. In addition, in this embodiment, the spring means 84 is thegas spring. Therefore, free vibration of the spring means 84 hardlyoccurs in the shift from the locked state to the free state. Thus, theshift from the free state to the locked state thereafter can beperformed smoothly, thereby generating the auxiliary knee rotation forcesmoothly.

[0145] Note that, in this embodiment, the pressurized gas is filled inboth of the gas chambers 91 and 92 within the cylinder 85. However, forexample, one of the gas chambers 91 and 92 may be opened to theatmosphere and the other chamber may be opened and closed to theatmosphere through a switch valve. Nevertheless, the configuration ofthe spring means in the aforementioned tenth embodiment is advantageousfor achieving spring means which has a relatively small configurationand is enabled to generate relatively large auxiliary knee rotationforce. Further, in this embodiment, the switch valve 93 is providedoutside of the cylinder 85, but may be provided in the piston 88.

[0146] Next, an eleventh embodiment of the present invention isdescribed with reference to FIGS. 22 and 23. Note that this embodimentis different from the foregoing first and second embodiments only inthat the mechanical configuration of the assist device. Thus, referencenumerals and figures the same as those for the first embodiment denoteconstituents and functional portions the same as those of the firstembodiment, and a description thereof is omitted.

[0147] Referring to FIG. 22, an assist device 95 of this embodiment isprovided with a gas spring having a cylinder structure as spring means96, and an accumulator 97 storing pressurized gas.

[0148] The spring means 96 has a basic configuration and an attachingstructure to the leg 3, which are similar to those of the spring means84 of the aforementioned tenth embodiment. The spring means 96 isconfigured by a cylinder (outer cylinder) 100 whose bottom portion isconnected to the crus portion 5 through a connecting rod 98 and a freejoint 99, a piston 101 slidable within the cylinder 100 in the axisdirection thereof, and a piston rod 103 extending from the piston 101toward the upper side and connected to the thigh portion 4 through afree joint 102. Gas such as air is filled in a gas chamber 104 under thepiston 101 (bottom part side of the cylinder 100) within the cylinder100. A gas chamber 105 above the piston 101 is opened to the atmosphere.In this case, in the assist device 95 of this embodiment, the gaschamber 104 within the cylinder 100 is connected to the aforementionedaccumulator 97 through a communicating pipe 107 having a switch valve106. Here, the switch valve 106 is an electromagnetic switch valve whichcan switch between a close state and an open state. In the close state,communications between the gas chamber 104 within the cylinder 100 andthe accumulator 97 is blocked. In the open state, the gas chamber 104and the accumulator 97 are allowed to communicate with each other. Theswitch valve 106 corresponds to the motion transmissioncontinuation/discontinuation means of the present invention. Note thatthe pressure of the pressurized gas in the accumulator 97 is set to beslightly higher than the atmospheric pressure (pressure in the gaschamber 104). Further, when the switch valve 106 is in the open state,the pressure of the pressurized gas in the accumulator 97 is set to bealmost equal to the atmospheric pressure, in a state where the kneebending angle θ is almost “0” (a state where the leg 3 is stretchedstraight) Furthermore, a check valve denoted by reference numeral 108 isrelated to a modified aspect of this embodiment, which will be describedlater.

[0149] In the assist device 95 having the above-mentioned configuration,a state where the switch valve 106 is actuated to the open state and astate where the switch valve 106 is actuated to the close statecorrespond to the free state and the locked state in the foregoing fistand second embodiments, respectively, similarly to the foregoing ninthor tenth embodiment. Specifically, in the state where the switch valve106 is actuated to the open state, the gas flows between the gas chamber104 within the cylinder 100 and the accumulator 97 in accordance with amovement of the piston 101 accompanying the knee bending and stretchingmotion of the leg 3. Thus, the spring means 96 does not generate largeelastic force (auxiliary knee rotation force) However, in thisembodiment, the pressure in the accumulator 97 communicating with thechamber 104 within the cylinder 100 is set as mentioned earlier in thefree state. Therefore, as shown by a broken line e in FIG. 23, thespring means 96 generates relatively small elastic force (auxiliary kneerotation force) as the knee bending angle θ increases. Further, in thelocked state (the close state of the switch valve 106), the pressurewithin the gas chamber 104 in the cylinder 100 increases/decreases inaccordance with a movement of the piston 101 accompanying the kneebending and stretching motion of the leg 3. Thus, the spring means 96generates relatively large auxiliary knee rotation force. As shown inFIG. 23, when the knee bending angles at the start time of the lockedstate (lock start knee bending angle) are, for example, θ5 and θ6, thecharacteristics of the auxiliary knee rotation force by the spring means96 relative to the knee bending angle θ in the locked state, are thecharacteristics shown by solid line f and g, respectively.

[0150] The configurations other than the above-described configurationare the same as those of the foregoing first and second embodiments. Inaddition, control processing by the control unit 27 is the same as thatof the foregoing first and second embodiments. However, in this case,similar to the case of the aforementioned ninth embodiment, the lockcommand transmitted by the lock mechanism controller 33 of the controlunit 27 is a command directing the switch valve 106 to the close state,and the free command is a command directing the switch valve 106 to bein the open state.

[0151] In the system of this embodiment described above, the lock periodis set similarly to the foregoing first and second embodiments, duringthe running motion of the robot 1. When the switch valve 106 is in theclose state (locked state) in the lock period, a large auxiliary kneerotation force can be generated by the spring means 96 in accordancewith the knee bending and stretching motion. Thus, the burden on theknee joint electric motor 10 can be further decreased. In this case, inthis embodiment, an elastic force by the spring means 96 is generatedeven in the free state and acts on the knee joint 8. However, theelastic force is sufficiently small. Therefore, it is unlikely that theburden on the knee joint electric motor 10 is greatly increased in thefree state.

[0152] Note that, in this embodiment, as shown by an imaginary line inFIG. 22, the check valve 108 may be connected in parallel with theswitch valve 106. In the case where the check valve 108 is provided asabove, when the knee bending angle θ becomes smaller than the kneebending angle at the start time of the locked state (lock start kneebending angle) in the locked state in which the switch valve 106 isdirected to the close state, a state the same as the free state isproduced. Thus, the characteristics of the auxiliary knee rotation forceby the spring means 96 relative to the knee bending angle θ in the closestate of the switch valve 106, are the characteristics shown by solidlines h and i in FIG. 24 (θ7 and θ8 are the lock start knee bendingangles). Specifically, when the knee bending angle θ is smaller than thelock start knee bending angles θ7 and θ8, the characteristics of theauxiliary knee rotation force by the spring means 96 are the same as thecharacteristics shown by the broken line e in the aforementioned FIG.23. When the knee bending angle θ is larger than the lock-start kneebending angles θ7 and θ8, the characteristics of the auxiliary kneerotation force by the spring means 96 are similar to the characteristicsshown by the solid lines f and g of the aforementioned FIG. 23. In thiscase, when the knee bending angle θ is smaller than the lock start kneebending angles θ7 and θ8, the auxiliary knee rotation force by thespring means 96 is sufficiently small. Thus, an effect of action similarto those of the foregoing third and fourth embodiments can be achieved.

[0153] Moreover, as shown in FIG. 25, the system having a function equalto that of the system in this embodiment (hereinafter, referred to as atwelfth embodiment) can be realized by connecting the free joints 13 and18 using a spring 109 (which may be any of a solid spring and a gasspring) with a relatively small elastic force, in the system shown inFIG. 1 (a system related to the foregoing first to four theembodiments). Here, in FIG. 25, portions the same as those of FIG. 1 aredenoted by the same reference numerals. Note that, in order to providethis embodiment (the twelfth embodiment) with the function equal to thatof the aforementioned eleventh embodiment, it is required to allow thespring 109 to constantly generate an elastic force in the stretchingdirection of the leg 3. However, it is also possible to allow the spring109 to generate the elastic force in the bending direction of the leg 3,which is an opposite direction to the stretching direction of the same(however, the elastic force is sufficiently smaller than the elasticforce by the spring means 15 in the locked state). In this case, theburden on the knee joint electric motor 10 can be reduced, for example,in the free leg period of the leg 3.

[0154] Next, a thirteenth embodiment of the present invention isdescribed with reference to FIGS. 26 and 27. Note that this embodimentis different from the foregoing first and second embodiments only in themechanical configuration of the assist device. Thus, reference numeralsand figures the same as those for the first embodiment denoteconstituents and functional portions the same as those of the firstembodiment, and a description thereof is omitted.

[0155] Referring to FIG. 26, an assist device 110 of this embodiment isprovided with an air motor (pump) 111 as the spring means, and anaccumulator 112 storing pressurized gas. As shown in FIG. 27, therotating shaft (not shown) of the air motor 111 is connected to the crusportion 5 through a speed reducer 113. Specifically, the rotating shaftportion 49 of the crus portion 5 is rotatably supported by the thighportion 4 through the bearing 50, similarly to the case of the foregoingsixth embodiment. Additionally, the end of the rotating shaft portion49, projecting to the outside of the thigh portion 4, is connected tothe output side of the speed reducer 113, and the input side of thespeed reducer 113 is connected to the rotating shaft (not shown) of theair motor 111. Here, the speed reducer 113 is for increasing therotation speed of the air motor 111 to be faster than the rotation speedof the rotating shaft portion 49 of the crus portion 5. Note that,although not illustrated in detail, the case of the air motor 111 isfixed to the thigh portion 4. Further, the air motor 111 is apositive-displacement motor which is, for example, a vane type motor ora swash plate type motor.

[0156] The air outlet of the air motor 111 is connected to theaforementioned accumulator 112 through a communicating pipe 115 having aswitch valve 114 which corresponds to the motion transmissioncontinuation/discontinuation means of the present invention. Here, theswitch valve 114 is an electromagnetic switch valve which can switchbetween a position A and a position B. At the position A, the air outletof the air motor 111 and the accumulator 112 are opened to theatmosphere. At the position B, the air outlet of the air motor 111 andthe accumulator 112 are allowed to communicate with each other. Notethat, the air inlet of the air motor 111 is opened to the atmosphere.

[0157] In the assist device 110 having the above-describedconfiguration, similar to the foregoing ninth and tenth embodiments, thestate where the switch valve 114 is actuated to be at the position A andthe state where the switch valve 114 is actuated to be at the position Bcorrespond to the free state and the locked state in the foregoing firstand second embodiments, respectively. Specifically, in the state wherethe switch valve 114 is actuated to be at the position A, the pressurewithin the air motor 111 does not rise by rotation of the rotating shaftof the air motor 111 due to the knee bending and stretching motion ofthe leg 3. Thus, the auxiliary knee rotation force does not act on theknee joint 8.

[0158] Meanwhile, in the state where the switch valve 114 is actuated tothe position B, air is pressured and sent to the accumulator 112 by therotation of the rotating shaft of the air motor 111 accompanying theknee bending and stretching motion of the leg 3, increasing the pressureof the air. Thus, the auxiliary knee rotation force acts on the kneejoint 8 through the rotating shaft of the air motor 111 and theforegoing speed reducer 113.

[0159] The configurations other than the above-described configurationare the same as those of the foregoing first and second embodiments. Inaddition, control processing by the control unit 27 is the same as thatof the foregoing first and second embodiments. In this case, however,the lock command transmitted from the lock mechanism controller 33 ofthe control unit 27 is a command causing the switch valve 114 to be atthe position B, and the free command is a command causing the switchvalve 114 to be at the position A. Therefore, the system of thisembodiment can realize an effect of action similar to those of theforegoing first and second embodiments.

[0160] Note that, when, for example, a swash plate type variabledisplacement motor (pump) is used as the air motor 111 in the assistdevice 110 having the configuration like the one shown in thisembodiment, the spring constant of the air motor 111 serving as thespring means can be changeable by adjusting the volume of the motor. Thechangeable spring constant of the spring means is feasible not only inthe assist device of this embodiment but also in those of the first totwelfth embodiments. For example, in the assist device having theconfiguration shown in FIG. 14, the connecting member 46 or the like maybe expanded/contracted and the length thereof (more strictly, thedistance between the free joint 45, a point of action of the force bythe spring means 15, and the center of rotation of the knee joint 8) isadjusted. Thus, the spring constant of the spring means 15 can bechangeable. This can be applied to those shown in FIGS. 1, 13, and 25.Moreover, in the assist device provided with the speed reducer 56 as theone shown in FIG. 16, a variable-speed speed reducer is employed and thespeed reducing ratio thereof is adjusted, thereby adjusting the springconstant. Furthermore, for example, in the assist device provided withthe cam 59 as the one shown in FIG. 18, the spring constant can beadjusted by providing cams having different cam shapes from each otherand providing means for switching between these cams. Yet further, forexample, in the assist device provided with the accumulator 97 as theone shown in FIG. 22, a plurality of accumulators are provided. Theseaccumulators communicate with each other and the communicationtherebetween can be blocked, through an open-close valve or the like.Thus, the effective capacity of the accumulators as a whole is adjusted,and thereby the spring constant can be adjusted. Yet further, forexample, in the assist device like the one shown in FIG. 21, in whichgas related to the spring means is sealed, the spring constant can beadjusted by changing the pressure of the gas by the use of an externalpump or the like.

[0161] Note that, in each of the first to thirteenth embodimentsdescribed so far, the assist device has been described, which causes theauxiliary knee rotation force by the spring means to act on the kneejoint 8 of the leg 3 as appropriate. However, the assist device of thepresent invention can also be applied to the ankle joint 9 and the hipjoint 7 of the leg 3. Moreover, the present invention can be applied notonly to the robot with legs, each having only the hip joint, the kneejoint, and the ankle joint as the joints thereof, but also to a robothaving more joints. In addition, the present invention can be appliednot only to the biped mobile robot, but also to a robot having more thanor equal to three legs.

[0162] Moreover, in each of the foregoing embodiments, the assist devicewas shown, in which the auxiliary knee rotation force by the springmeans is generated as appropriate during the running motion of the robot1. However, the assist device is not limited to the above. The presentinvention may also be applied for a gait in ascent and decent of stairsor the like, which causes a situation where a driving force to begenerated to a joint becomes relatively large.

[0163] Moreover, in the assist device as the one shown in FIG. 21,provided with the spring means 84, which is an air spring, and theswitch valve 93, it is possible to provide a cam at the knee joint sothat the knee bending and stretching motion is transmitted to the springmeans 84 by the cam. In this case, it is also possible to accommodatethe spring means 84 within the thigh portion 4.

[0164] Furthermore, the spring means of the present invention may beconfigured by connecting a plurality of solid springs or gas springs inseries.

Industrial Applicability

[0165] As hitherto described, the present invention is useful as it canreduce the burden on the joint actuator while the legged mobile robotsuch as the biped mobile robot is moving, thereby providing the leggedmobile robot with less energy loss.

1. A leg joint assist device for generating an auxiliary driving forceon a specific joint of a legged mobile robot in parallel with a drivingforce of a joint actuator driving the specific joint, the robotcomprising a plurality of legs, extending from a body, configured byconnecting a plurality of link members sequentially from a body sidethrough the plurality of joints, wherein at least one joint amongst aplurality of the joints of each of a plurality of the legs is defined asthe specific joint in the legged mobile robot, the leg joint assistdevice comprising: spring means, provided to be able to transmit arelative displacement motion of a pair of the link members connected bythe specific joint, the relative displacement motion being caused byactuation of the specific joint, for generating the auxiliary drivingforce while storing elastic energy in synchronization with the relativedisplacement motion in a state where transmission of the relativedisplacement motion is continued, and for restoring a state where theelastic energy is released in a state where transmission of the relativedisplacement motion is discontinued; motion transmissioncontinuation/discontinuation means for continuing and discontinuingtransmission of the relative displacement motion of the pair of linkmembers to the spring means; and control means for controllingcontinuation/discontinuation of transmission of the relativedisplacement motion to the spring means by the motion transmissioncontinuation/discontinuation means, depending on a state of motion ofeach of the legs.
 2. The leg joint assist device according to claim 1,wherein the control means controls the motion transmissioncontinuation/discontinuation means to discontinue transmission of therelative displacement motion of the pair of link members to the springmeans at least during a first predetermined period in a state where eachof the legs is lifted off a floor.
 3. The leg joint assist deviceaccording to claim 1, wherein, while the legged mobile robot is movingwith a predetermined gait which has been decided in advance, the controlmeans controls the motion transmission continuation/discontinuationmeans to continue transmission of the relative displacement motion ofthe pair of link members to the spring means at least during a secondpredetermined period in a state where each of the legs lands on thefloor.
 4. The leg joint assist device according to claim 3, wherein thesecond predetermined period in the state where each of the legs lands onthe floor is determined such that relative displacement amounts betweenthe pair of link members at start time and stop time of the secondpredetermined period are approximately equal.
 5. The leg joint assistdevice according to claim 3, comprising means for controlling a drivingforce of the joint actuator such that, while the motion transmissioncontinuation/discontinuation means is continuing transmission of therelative displacement motion of the pair of link members to the springmeans, a sum of the auxiliary driving force by the spring means and thedriving force of the joint actuator becomes a desired driving forcedetermined to follow a desired gait of the legged mobile robot.
 6. Theleg joint assist device according to claim 5, wherein the means forcontrolling the driving force of the joint actuator estimates theauxiliary driving force by the spring means based on a variation of therelative displacement amount between the pair of link members from thestart time of the second predetermined period and characteristic data ofthe auxiliary driving force of the spring means, which is obtained inadvance.
 7. The leg joint assist device according to claim 1, whereinthe spring means is a gas spring which elastically generates theauxiliary driving force by compression or expansion of gas.
 8. The legjoint assist device according to claim 1, wherein the joint actuator isan electric motor.
 9. The leg joint assist device according to claim 2,wherein, while the legged mobile robot is moving with a predeterminedgait which has been decided in advance, the control means controls themotion transmission continuation/discontinuation means to continuetransmission of the relative displacement motion of the pair of linkmembers to the spring means at least during a second predeterminedperiod in a state where each of the legs lands on the floor.
 10. The legjoint assist device according to claim 9, wherein the secondpredetermined period in the state where each of the legs lands on thefloor is determined such that relative displacement amounts between thepair of link members at start time and stop time of the secondpredetermined period are approximately equal.
 11. The leg joint assistdevice according to claim 9, comprising means for controlling a drivingforce of the joint actuator such that, while the motion transmissioncontinuation/discontinuation means is continuing transmission of therelative displacement motion of the pair of link members to the springmeans, a sum of the auxiliary driving force by the spring means and thedriving force of the joint actuator becomes a desired driving forcedetermined to follow a desired gait of the legged mobile robot.
 12. Theleg joint assist device according to claim 11, wherein the means forcontrolling the driving force of the joint actuator estimates theauxiliary driving force by the spring means based on a variation of therelative displacement amount between the pair of link members from thestart time of the second predetermined period and characteristic data ofthe auxiliary driving force of the spring means, which is obtained inadvance.
 13. The leg joint assist device according to claim 9, whereinthe spring means is a gas spring which elastically generates theauxiliary driving force by compression or expansion of gas.
 14. The legjoint assist device according to claim 9, wherein the joint actuator isan electric motor.